Opinion of the Court by
MOON, C.J.
Plaintiffs-appellants, approximately 322 unaffiliated Hawaii health care providers [hereinafter, collectively, the providers], bring this interlocutory appeal pursuant to Hawaii Revised Statutes (HRS) § 641-l(b) (1993),1 challenging the August 30, 2001 non-final appealable ruling of the Circuit Court of the First Circuit, the Honorable Virginia L. Crandall presiding, denying their motion for partial summary judgment and granting partial summary judgment in favor of defendants-appellees automobile insurers and adjusters [hereinafter, collectively, the insurers].2
On appeal, the providers argue that the circuit court erred in: (1) finding that the written notice of denial of benefits mandated by HRS § 431:10C-304(3)6b) (1993), quoted infra, [hereinafter, HRS § 43L10C-304(3)(B), Section (3)(B), or the subject stat[191]*191ute] is inapplicable to the subject billing disputes; (2) concluding that Hawai'i Administrative Rules (HAR) § 16-23-120 (1993), quoted infra, applies; and (3) retroactively applying the May 30, 2000 legislative amendments to the subject statute and the September 18, 2000 Insurance Commissioner’s Order in GEICO v. Dep’t of Commerce & Consumer Affairs (DCCA), INS-DR-2001-1.
For the reasons discussed herein, we vacate the circuit court’s August 30, 2001 order denying the providers’ motion for partial summary judgment and granting partial summary judgment in favor of the insurers and remand this case for further proceedings consistent with this opinion.
I. BACKGROUND
A. Factual Background
The facts of this case are uncontested. Between January 1, 1993 and December 31, 1999, each of the providers submitted bills to one or more of the insurers for non-emergency treatments rendered to thousands of personal injury protection (PIP) insureds allegedly injured in motor vehicle accidents. The insurers were obligated to pay appropriate PIP benefits under HRS chapter 431:10C on behalf of their insureds. For purposes of billing, the existing workers’ compensation fee schedule was adopted as the payment fee schedule applicable to medical and rehabilitative services provided as no-fault benefits for persons injured in automobile accidents. HRS §§ 431:10C-308.5(a) and (b) (1993). Under section 431:10C-308.5(a), “the term ‘workers’ compensation schedules’ means the schedules adopted and ... establishing [the] fees and frequency of treatment guidelines.” The workers’ compensation schedule assigns a medical procedure code and a fee to each item of service rendered by health care providers. The providers, in preparing their bills for submission to the insurers, are required to follow the “fees and frequency of treatment guidelines” contained in the workers’ compensation schedules. HRS § 431:10C-308.5(b). The insurers, however, rather than pay the bills as submitted, or deny the claim (in whole or in part), altered the treatment code because they believed that, “[biased on the available information, the services rendered appear to be best described by [a different medical treatment] code.” The resulting effect of changing the treatment codes was a reduction in the payment for the service rendered, which the parties generally refer to as “down-coding.”3 The insurers, thus, (1) paid the bills pursuant to the adjusted treatment codes and (2) offered to negotiate with the providers as to the unpaid portions.
B. Procedural Background
On April 15, 1998, the providers filed a complaint against the insurers for the alleged underpayment for services rendered under their respective no-fault insurance contracts. Count I alleged that the insurers unlawfully down-coded, thereby reducing the amounts of the providers’ bills without issuing denial letters, in violation of HRS § 431:10C-304(3)(B), or seeking peer review, as required by HRS § 431:100-308.6 (1993).4 [192]*192Count II alleged that the insurers breached their no-fault insurance contracts by failing or refusing to pay for services rendered.5 The complaint sought declaratory and injunc-tive relief against down-coding of the providers’ bills and damages for the underpaid amounts of the bills. The providers’ complaint involves disputes regarding over 30,-000 bills, approximately 10,000 of which have been produced in discovery.
In May 2000, Act 138 was signed into law, which amended HRS §§ 431:100-304 and 431:100-308.5 by, among other things, adding section 6 to HRS § 431:100-304 and section (e) to HRS § 431:100-308.5. Section 4 of the act stated that “[tjhis Act shall take effect upon its approval.” 2000 Haw. Sess. L. Act 138, § 4 at 271. The act was approved on May 30, 2000. Id. The new sub-paragraph (6) of HRS § 431:100-304 (Supp. 2004) states:
Disputes between the provider and the insurer over the amount of a charge or the correct fee or procedure code to be used under the workers’ compensation supplemental medical fee schedule shall be governed by section 431:10C-308.5[.]
HRS § 431:10C-308.5(e) (Supp.2004) states:
In the event of a dispute between the provider and the insurer over the amount of a charge or the correct fee or procedure code to be used under the workers’ compensation supplemental medical fee schedule, the insurer shall:
(1) Pay all undisputed charges within thirty days after the insurer has received reasonable proof of the fact and amount of benefits accrued and demand for payment thereof; and
(2) Negotiate in good faith with the provider on the disputed charges for a period up to sixty days after the insurer has received reasonable proof of the fact and amount of benefits accrued and demand for payment thereof.
If the provider and the insurer are unable to resolve the dispute, the provider, insurer, or claimant may submit the dispute to the commissioner, arbitration, or court of competent jurisdiction. The parties shall include documentation of the efforts of the insurer and the provider to reach a negotiated resolution of the dispute.
Thereafter, on January 10, 2001, the providers moved for summary judgment on Count I as to eleven bills, involving five providers and ten insurers, for services rendered between May 28, 1993 and August 5, 1998. The providers asserted that these bills were unlawfully reduced twenty to sixty percent by down-coding and without complying with certain statutory provisions. The providers specifically contended that: (1) the insurers’ practice of “unilaterally changing] the medical procedure codes or refus[ing] to pay the procedure codes, as submitted, to reduce the overall amount of the bill[,]” was “illegal[,]” because such practice is contrary [193]*193to the peer review procedure mandated by HRS § 431:100-308.6; and (2) the insurers were in technical violation of Section (3)(B) for failure to provide written notices of their denials of all or part of a claim within the mandated period.
On February 2, 2001, the insurers filed cross-motions for partial summary judgment on Count I as to the eleven bills, arguing that the bills were lawfully adjusted and that the underpayments were negotiable. The insurers averred that, because they accepted all treatments rendered in connection with the eleven bills as reasonable, necessary, and appropriate, they were not obligated to issue a written denial pursuant to Section (3)(B) or seek peer review under HRS § 431:10C-308.6. The insurers sought a ruling, as a matter of law, that they utilized the correct billing dispute resolution mechanism when they paid the undisputed portion of the bills at issue and offered to negotiate the remaining balance in accordance with HAR § 16-23-120 and the 2000 amendment to HRS § 431:10C-308.5. In support of their position, the insurers relied upon (1) the Insurance Commissioner’s Order in GEICO, issued on September 18, 2000, adopting the insurers’ position in its entirety and (2) the May 30, 2000 legislative amendments to HRS §§ 431:10C-304 and 431:100-308.5.
After a hearing on February 23, 2001 on both motions, the circuit court, in its minute order of August 3, 2001, denied the providers’ motion for partial summary judgment and granted the insurers’ cross-motion, essentially adopting the insurers’ arguments, namely, that HRS §§ 431:100-304 and 431:100-308.6 are inapplicable to the facts of this case and that HAR § 16-23-120 applies. On August 30, 2001, the court entered it written ruling, wherein it found and concluded that
the bills at issue herein are billing disputes where the insurer has accepted the treatment as reasonable and appropriate and has paid the undisputed amount of the bill and are not bills for which the [insurers] were required to issue a formal denial or seek peer review of the billing disputes. Further, the Court finds that the “72-hour treatment” cases are inapposite to the instant matter. [HAR] Sec. 16-23-120 (1993) applies. The Court holds that the [insurers] utilized the correct billing] dispute mechanism.[6]
In the meantime, the providers, on August 27, 2001, filed a motion for clarification of the circuit court’s minute order. The motion sought to clarify that the court’s order applied to only those billing disputes arising after January 1, 1998, the date the peer review statute was repealed. The court denied the motion on October 15, 2001.
Prior to the denial of their motion for clarification, the providers, on September 14, 2001, filed a motion for certification of the order granting the insurers’ cross-motion for partial summary judgment and denying the providers’ motion, pursuant to Hawai'i Rules of Civil Procedure (HRCP) Rule 54(b) (2000),7 or, in the alternative, for leave to file interlocutory appeal.8 After a hearing on [194]*194September 27, 2001, the circuit court filed its order, dated October 1, 2001, denying the providers’ request for HRCP Rule 54(b) certification, but granting leave to file an interlocutory appeal, finding that,
under the specific circumstances of this case[,] a significant ruling has been issued on the billing] dispute mechanism and that an interlocutory appeal will provide for a speedier termination of the litigation.
On October 18, 2001, the providers filed a timely notice of appeal.9
II. STANDARDS OF REVIEW
A. Summary Judgment
“We review the circuit court’s grant or denial of summary judgment de novo.” Yamagata v. State Farm Mut. Auto. Ins. Co., 107 Hawai'i 227, 229, 112 P.3d 713, 715 (2005) (citing Hawai'i Cmty. Fed. Credit Union v. Keka, 94 Hawai'i 213, 221, 11 P.3d 1, 9 (2000)). The standard for granting a motion for summary judgment is well established:
[SJummary judgment is appropriate if the pleadings, depositions, answers to interrogatories, and admissions on file, together with the affidavits, if any, show that there is no genuine issue as to any material fact and that the moving party is entitled to judgment as a matter of law. A fact is material if proof of that fact would have the effect of establishing or refuting one of the essential elements of a cause of action or defense asserted by the parties. The evidence must be viewed in the light most favorable to the non-moving party. In other words, we must view all of the evidence and the inferences drawn therefrom in the light most favorable to the party opposing the motion.
Querubin v. Thronas, 107 Hawai'i 48, 56, 109 P.3d 689, 697 (2005) (citations omitted) (brackets in original).
B. Statutory Interpretation
“Questions of statutory interpretation are questions of law to be reviewed de novo under the righf/wrong standard.” Guth v. Freeland, 96 Hawai'i 147, 149-50, 28 P.3d 982, 984-85 (2001) (citations omitted).
III. DISCUSSION
As previously stated, the providers, on appeal, advance three points of error regarding the circuit court’s order denying their motion for partial summary judgment and granting the insurers’ cross-motion, alleging that the circuit court erred in: (1) finding that the insurers were not required to issue formal written notices of denial for partial payment of medical bills pursuant to HRS § 431:10C-304(3)(B); (2) ruling that HAR § 16-23-120 applies to the subject billing disputes;10 and (3) relying on the subsequent legislative amendments and the Insurance Commissioner’s decision in GEICO for any medical bill submitted prior to May 30, 2000.
A. Applicability of HRS § US1:10-S0I(S)(B)
Preliminarily, we note that an insurer’s obligation to pay no-fault benefits11 is set [195]*195forth in HRS § 431:10C-304(3)(A), which provides that “[p]ayment of no-fault benefits shall be made within thirty days after the insurer has received reasonable proof of the fact and amount of benefits accrued, and demand for payment thereof.” (Emphasis added.) In other words, an insurer shall pay no-fault benefits within thirty days of receipt of a provider’s billing statement showing “the fact,” ie., the treatment services, and “the amount of benefits,” ie., the charges or cost of treatment services.
At the time the providers’ claims arose, Section (3)(B) provided:
(B) Subject to section 431:10C-308.6, relating to peer review, if the insurer elects to deny a claim for benefits in whole or in part, the insurer shall within thirty days notify the claimant in ivriting of the denial and the reasons for the denial. The denial notice shall be prepared and mailed by the insurer in triplicate copies and be in a format approved by the commissioner. In the case of benefits for services specified in section 431:10C-103(10)(A)(i) and (ii) the insurer shall also mail a copy of the denial to the provider.
(Emphases added.) The providers maintain that the subject statute clearly sets forth the applicable procedure when an insurer wishes to deny “a claim for benefits,” that is, treatment services and/or costs, “in whole or in part” and that any partial payment of medical bills constitutes a denial and triggers the insurer’s obligation under the statute to provide written notice within thirty days. In response, the insurers assert that, where they have accepted the treatment rendered as reasonable and appropriate and the sole dispute concerns the appropriate charges for that treatment, such dispute is outside the scope of the subject statute. Thus, the dis-positive issue on appeal is whether “a claim for benefits” under HRS § 431:10C-304(3)(B) encompasses treatment services and the costs attendant thereto such that a denial of services and/or costs, in whole or in part, triggers the notice requirement specified in the statute.
We begin our analysis by examining the plain language of the statute at issue. Zanakis-Pico v. Cutter Dodge, Inc., 98 Hawai'i 309, 316, 47 P.3d 1222, 1229 (2002). In so doing, “our foremost obligation is to ascertain and give effect to the intention of the legislature, which is to be obtained primarily from the language contained in the statute itself.” Yamagata, 107 Hawai'i at 229, 112 P.3d at 715 (citations omitted); see also Allstate Ins. Co. v. Schmidt, 104 Hawai'i 261, 265, 88 P.3d 196, 200 (2004) (“[W]here the language of the statute is plain and unambiguous, our only duty is to give effect to its plain and obvious meaning.” (Citations omitted.) (Brackets in original.)).
As previously indicated, the insurers maintain that they were not obligated to provide notice because the sole dispute centered around the charges and not the treatment services. Section (3)(B), however, does not limit an insurer’s obligation to provide notice only when the insurer elects to deny a claim for treatment services. In reading the first and second sentence of Section (3)(B), it is clear that “a claim for benefits” includes both treatment services and the charges attendant thereto. The first sentence of Section (3)(B) indicates that any denial of “a claim for benefits,” either in whole or in part, requires the issuance of a denial notice to the claimant.12 The second sentence states: “In the case of benefits for services ... the insurer shall also mail a copy of the denial to the provider.” (Emphases added.) In other words, if an insurer elects to deny a claim for treatment services and/or cost, in whole or in part, it must notify the claimant; if the denial involves treatment services, the insurer— in addition to notifying the claimant—must also notify the provider of the denial. If we were to limit the phrase “claim for benefits” [196]*196as used in the first sentence of Section (3)(B) to treatment services only, as the insurers urge, the second sentence would be rendered superfluous. See In re City & County of Honolulu Corp. Counsel, 54 Haw. 356, 373, 507 P.2d 169, 178 (1973) (applying the “cardinal rule of statutory construction that a statute ought upon the whole be so constructed that, if it can be prevented, no clause, sentence or word shall be superfluous, void, or insignificant” (citations omitted) (emphases added)).
We further note that nowhere in HRS § 431:100-304 does it authorize the insurers to down-code the billings. In fact, HRS § 431:10C-304(3)(C) specifically provides:
If the insurer cannot pay or deny the claim for benefits because additional information or loss documentation is needed, the insurer shall, within thirty days, forward to the claimant an itemized list of all the required documents. In the case of benefits for services specified in section 431:10C-103(A)(i) and (ii) [see supra note 13], the insurer shall also forward the list to the service provider.
(Emphases added.) Inasmuch as the insurers’ down-coding was based on lack of sufficient information to support the declared treatment code, the insurers were required to forward to the claimant and the provider “an itemized list of all the required documents.”
In light of the unambiguous mandatory language of HRS § 431:10C-304(3)(B), an insurer is required to provide written notice of its denial—in whole or in part—of the claim for benefits. Written notice to the claimant is required where the denial or partial denial relates to the treatment service and/or the charges therefor. Where the denial or partial denial involves treatment services, the insurer must also provide written notice to the provider. We, therefore, hold that the circuit court erred in ruling that “billing disputes where the insurer[s] ha[ve] accepted the treatment as reasonable and appropriate and ha[ve] paid the undisputed amount of the bill ... are not bills for which the [insurers] were required to issue a formal denial [in accordance with Section (3)(B).]”
B. Applicability of HAR § 16-23-120
The providers next contend that the circuit court erroneously concluded that HAR § 16-23-120 applies to the instant billing disputes. The insurers maintain that HAR § 16-23-120, which provides a billing dispute resolution mechanism, controls and that, therefore, the billing disputes at issue fall outside the purview of HRS § 431:10C-304(3)(B).
HAR § 16-23-120, entitled “Dispute Regarding Charges,” adopted by the Insurance Commissioner in 1993, provides in pertinent part:
(a) In the event of a dispute between the provider and the insurer over the amount of a charge or the correct fee and procedure code to be used pursuant to Exhibit “A” to the workers’ compensation schedules, the insurer shall pay all charges not in dispute and shall negotiate in good faith with the provider on the disputed charges. Such disputes shall not be filed with the commissioner for submission to peer review.
(b) If the provider and the insurer cannot resolve the dispute, either party may make a request to the commissioner for a hearing.
(Emphases added.) We recognize that the Insurance Commissioner has the authority to promulgate administrative rules pursuant to HRS § 431:10C-214 (1993)13 and, most significantly, “to adopt administrative rules relating to fees or frequency of treatment” as permitted by HRS § 431:10C-308.5(b). We also recognize that ah administrative agency’s interpretation of its own rules “is normally accorded great weight.” Coon v. City & County of Honolulu, 98 Hawai'i 233, 251, [197]*19747 P.3d 348, 366 (2002). However, “[i]t is axiomatic that an administrative rule cannot contradict or conflict with the statute it attempts to implement.” Agsalud v. Blalack, 67 Haw. 588, 591, 699 P.2d 17, 19 (1985) (citations omitted). Pursuant to HRS § 91-7(b) (1993), this court “shall declare the [administrative] rule invalid if it finds that it violates ... statutory provisions, or exceeds the statutory authority of the agency, or was adopted without compliance with statutory rulemaking procedures.” See also In re Water Use Permit Applications, 94 Hawai'i 97, 145, 9 P.3d 409, 457 (stating that “we have not hesitated to reject an incorrect or unreasonable statutory construction advanced by the agency entrusted with the statute’s implementation”), reconsideration denied, as amended, 94 Hawai'i 97, 9 P.3d 409 (2000).
Under HAR § 16-23-120, disputes relating to “the amount of a charge or the correct fee and procedure code” need not “be filed with the [Insurance] Commissioner for submission to [p]eer [r]eview.” Rather, it authorizes insurers to make partial payment of charges “not in dispute” and negotiate with the providers on “the disputed charges.” The peer review exemption, however, clearly conflicts with the plain language of HRS § 431:10C-304(3)(B) that was in existence before the repeal of the peer review statute. Prior to the repeal, an insurer’s denial of benefits, in whole or in part, was “[s]ubjeet to section 431:100-308.6, relating to peer review.” HRS § 431:10C-304(3)(B). Inasmuch as HAR § 16-23-120 exempts insurers from the peer review procedure for controversies relating to treatment services and/or the costs attendant thereto, we hold that HAR § 16-23-120 contravenes the express requirement of Section (3)(B) and is therefore void and unenforceable to this limited extent.
As a result of the January 1,1998 repeal of the peer review statute, the legislature deleted the phrase “[s]ubjeet to section 431:10C-308.6, relating to peer review” from Section (3)(B) as part of the 2000 amendments to HRS § 431:100-304. Thus, an insurer’s denial or partial denial of a claim for benefits is no longer subject to peer review.14 Accordingly, HAR § 16-23-120 does not conflict with the plain language of the subject statute as of the repeal date of the peer review statute. However, we emphasize that nothing in HAR § 16-23-120(1) relieves the insurers of their obligation to provide the written notice required by HRS § 431:100-304(3) (B) when the insurer wishes to challenge, in whole or in part, a bill for medical treatment or (2) authorizes the insurers’ practice of down-coding. Accordingly, to the extent that HAR § 16-23-120 is consistent with the subject statute after January 1, 1998, we hold that the insurers remain obligated to provide formal denial notices of a claim for benefits in accordance with Section (3)(B).
C. Retroactivity of the 2000 Amendments and GEICO v. DCCA
The providers argue that, in concluding that HAR § 16-23-120 applies, the circuit court erred in retrospectively applying (1) the subsequent legislative amendments to HRS §§ 431:100-304 and 431:100-308.5 as well as (2) the Insurance Commissioner’s Order in GEICO issued on September 18, 2000. In support of their contention, they point to the August 30, 2001 order. The order, however, made no reference to the amendments or the GEICO decision, and it is unclear from the record whether the circuit court relied, if at all, upon them. Because the providers did not direct us to anywhere else in the record that demonstrates the circuit court retroactively applied the amendments or the decision, we believe they have failed to meet their burden of showing that the circuit court erred. Ala Moana Boat Owners’ Ass’n v. State, 50 Haw. 156, 159, 434 P.2d 516, 518, reh’g denied, 50 Haw. 181, 434 P.2d 516 (1967); see also In re Estate of Lee Chuck, 33 [198]*198Haw. 445, 451-52 (1935) (“[There is] a general presumption ... in all legal proceedings that judicial tribunals ... act according to law. On appeal ... from the decision of an inferior judicial tribunal an appellate court will presume in review that it has complied with all the requirements of law and that its determination rested on facts sufficient to sustain them.” (Citations omitted.)).
IV. CONCLUSION
In light of the foregoing, we vacate the First Circuit Court’s August 30, 2001 order denying the providers’ motion for partial summary judgment and granting partial summary judgment in favor of the insurers, and remand this case to the circuit court for further proceedings consistent with this opinion.