Medicare Supplement (Medigap) Claim Denied: Appeal

Medicare Supplement plans — commonly called Medigap — are designed to work automatically alongside Original Medicare, picking up the costs that Medicare leaves behind. When a Medigap claim is denied, it is often a billing or coordination of benefits error rather than a genuine coverage dispute. Here is how to identify the problem and fix it.

How Medigap Works as a Secondary Payer

Medigap is sold by private insurance companies to cover costs that Original Medicare does not pay in full — primarily deductibles, coinsurance, and copayments. Medigap plans are standardized by the federal government into named plan types (Plan G, Plan N, Plan F, etc.), so the same Plan G from two different insurers provides identical benefits.

The payment process works like this:

1. Medicare processes your claim and pays its share (typically 80% for Part B services)
2. Medicare automatically "crosses over" the claim to your Medigap insurer
3. Your Medigap insurer pays its share based on your plan type

Because Medicare and Medigap share an automated crossover system, most Medigap claims are processed without you doing anything. When something goes wrong, it is almost always a coordination issue.

Why Medigap Claims Get Denied

1. Medicare Denied the Underlying Claim Medigap only pays when Medicare pays. If Medicare denied the underlying claim, Medigap has nothing to supplement — it will issue its own denial. In this case, your appeal should target the Medicare denial, not the Medigap denial. Once Medicare pays, Medigap should follow automatically.

2. Wrong Plan Letter Submitted There are multiple Medigap plan types (Plan A, B, D, G, K, L, M, N, and the grandfathered Plan C and F). If the claim was billed under the wrong plan letter or the insurer has incorrect plan information on file, the denial may be a simple administrative error.

3. Crossover Failure Sometimes the automatic Medicare-to-Medigap crossover fails — the claim doesn't transmit electronically. In this case, you can submit the claim manually to your Medigap insurer using your Medicare Summary Notice (MSN) as documentation.

4. Medicare Number or Enrollment Data Mismatch If your Medicare number, Medigap policy number, or enrollment dates are mismatched in the system, claims may be rejected. Call your Medigap insurer to verify they have your correct Medicare number.

5. Provider Not Enrolled in Medicare Medigap covers Medicare-covered services. If your provider is not enrolled in Medicare, Medicare won't pay — and Medigap won't pay. Verify your provider's Medicare enrollment before receiving non-emergency care.

6. Service Not Covered by Medicare Medigap cannot expand coverage beyond what Medicare covers. Services not covered by Medicare (routine dental, vision, hearing, long-term custodial care) are not covered by Medigap, regardless of your plan type.

What to Do When Medigap Won't Pay

Step 1 — Check Your Medicare Summary Notice (MSN) Review your MSN (mailed quarterly by Medicare) or log in to medicare.gov to see what Medicare paid on the claim. If Medicare paid its share, Medigap should follow. If Medicare denied the claim, address the Medicare denial first.

Step 2 — Call Your Medigap Insurer Call the insurer and ask specifically why the claim was denied. Request a reference number for the call. In many cases, you will identify the problem (crossover failure, wrong policy number, etc.) on this call.

Step 3 — Submit the Claim Manually If the crossover failed, submit the claim manually. Most Medigap insurers accept the MSN along with the EOB)" class="auto-link">Explanation of Benefits (EOB) from your provider as the basis for a manual claim.

Step 4 — File a Formal Appeal If the denial is not resolved by the above steps, file a formal appeal with the Medigap insurer in writing. Include your Medicare Summary Notice, the provider's claim documentation, and a clear explanation of why the denial is incorrect.

Step 5 — File a State Insurance Department Complaint Unlike Medicare Advantage plans (which are regulated by CMS), Medigap plans are regulated primarily by state insurance departments. If your Medigap insurer is refusing to pay a legitimate claim, file a complaint with your state's Department of Insurance (DOI). State insurance commissioners have enforcement authority over Medigap insurers.

Find your state DOI at the NAIC consumer information center (naic.org) or by searching "[your state] Department of Insurance."

SHIP Counselors for Medigap Issues

SHIP counselors are specially trained in Medigap rules and can help you identify whether a denial is a billing error, a coverage question, or an insurer compliance issue. Find your state SHIP at shiphelp.org or call 1-800-MEDICARE.

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Related Reading:

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs External Insurance Appeal