Was this for the retroactive ARA change in the reportable amount of unemployment benefits for TY 2020? Make sure that it is applicable to your income range.
IRS.gov - IRS offers overview of tax provisions in American Rescue Plan; retroactive tax benefits he... -
Notice that this IRS notice says:
Retroactive changes for 2020
Some unemployment compensation not taxed for many
For tax year 2020 only, the first $10,200 of unemployment compensation is not taxable for most households. This tax benefit is only available to those whose modified adjusted gross income is below $150,000 during 2020. The same income cap applies to all filing statuses.
This means that those eligible who haven't filed a 2020 return yet can subtract the first $10,200 from the total compensation received and only include the difference in their taxable income. For couples where both spouses received unemployment compensation, each spouse can subtract $10,200. Details, including a worksheet, are available at IRS.gov/form1040.
For any eligible taxpayer who has already filed and reported their compensation as fully taxable, the IRS is automatically adjusting their return and providing them this tax benefit. Refunds, based on this adjustment, are being issued in May and continuing through the summer.
If this is the reason, whether the IRS adjusted this amount "in-house", or you filed an amended return or you did the worksheet (see the embedded IRS links above)- that is the proof that you need, along with the above IRS newsroom advisory.
You can file an appeal with this info to back up your claim:
HHS.gov - Medicare Part B Premium Appeals
Hope this helps - Good Luck -
It's Always Something . . . . Roseanna Roseannadanna