Medigap Didn't Pay After Medicare

What This Means

Medicare processed your claim, approved the service, and paid its share. But the remaining balance — the part your Medigap supplement is supposed to cover — never made it to your supplement plan. Now your provider is billing you for that leftover amount.

This is not a denial. Medicare covered the service. The problem is that the payment pipeline between Medicare and your Medigap plan broke down somewhere along the way. Your supplement should be picking up most or all of the remaining cost, but it can’t pay a claim it never received.

The good news is that this is one of the easiest problems to fix. In most cases, a single phone call to your Medigap plan or your provider’s billing office will get things moving again.

Why This Happens

• The “crossover” system didn’t transmit the claim. Medicare is supposed to automatically send claim information to your Medigap plan through an electronic system officially known as the Coordination of Benefits Agreement (COBA) crossover process, run by the Benefits Coordination & Recovery Center. Sometimes that transmission fails or gets delayed, and your supplement never receives the claim.
• Your provider doesn’t have your Medigap plan on file. If the provider’s billing office doesn’t know you have a supplement, they won’t set up the crossover and may bill you directly for the remaining balance.
• Your Medigap plan has a processing delay. Even when the claim crosses over correctly, your supplement may take several weeks to process it. The provider may send you a bill before the supplement has finished paying.
• You recently enrolled in or changed your Medigap plan. If you switched supplement plans, the crossover system may still be linked to your old plan, or the new plan may not yet be registered in Medicare’s system.
• The claim information was incomplete. Occasionally, the crossover data is missing a piece of information your Medigap plan needs to process the claim, such as your policy number or the Medicare-approved amount.

Should You Appeal?

What To Do Next

1. Find your Medicare Summary Notice (MSN). Look for the claim in question. It should show the service, the Medicare-approved amount, what Medicare paid, and the remaining balance. You’ll need this information when you call your Medigap plan.
2. Call your Medigap plan. The customer service number is on the back of your supplement card. Ask if they received the claim from Medicare. If they say no, give them the claim number from your MSN and ask them to request the crossover data from Medicare.
3. Call your provider’s billing office. Let them know you have Medigap coverage and that the claim needs to cross over to your supplement. Ask them to submit the claim directly to your Medigap plan if the crossover didn’t work. Give them your supplement plan’s name, policy number, and group number.
4. Ask the provider to hold the bill. While the crossover issue is being resolved, ask the billing office to put a hold on your account so the bill doesn’t get sent to collections. Explain that your Medigap plan is processing the claim.
5. Follow up in two to three weeks. If you haven’t received an Explanation of Benefits from your Medigap plan showing they paid the claim, call them again to check on the status. Keep notes of every call — the date, who you spoke with, and what they said.
6. If all else fails, file a claim yourself. Most Medigap plans allow you to submit a claim on paper. You’ll need a copy of your MSN and the provider’s itemized bill. Your supplement plan can tell you exactly what to send and where to mail it.

Sources

• Medicare.gov: What’s Medicare Supplement Insurance (Medigap)? — overview of how Medigap works with Original Medicare.
• Medicare.gov: Compare Medigap Plan Benefits — what each lettered plan covers, including the Plans C and F restriction for people new to Medicare on or after January 1, 2020.
• CMS: Coordination of Benefits (COBA) overview — how Medicare transmits claims to Medigap and other secondary payers.
• CMS: 2026 Medicare Parts A & B Premiums and Deductibles — primary source for the 2026 Part B annual deductible ($283) referenced in the FAQ.
• Medicare.gov: Your Medicare Summary Notice — how to read your MSN and find the claim number you’ll need when you call your Medigap plan.
• X12: Claim Adjustment Reason Codes — official CARC definitions, including OA-23 (“impact of prior payer adjudication”) that typically appears on the provider’s secondary-payer EOB in this scenario.

Frequently Asked Questions