You wouldn't need to enter a refunded amount to Medicare Part B, since they simply refunded an amount you overpaid.
But tax withheld? I don't understand. Did you receive a tax document reporting the refund and tax withheld?
When the Social Security Administration refunded the Part B premium, they withheld Federal income taxes. That amount of tax was not included on the SSA statement. Nor was the refund included on the 1099.
@bogeyman62 So here's what must have happened:
Your Medicare Part B payment was withheld from your SS payment pre-tax. So when they refunded it, they withheld the tax that would have been due on the amount of your refund. (Based on what calculation...I have no idea).
I'm assuming you haven't received any type of tax document (separate from you SSA-1099) relating to this refund/tax withholding. There must be some way to report, at least, the income tax withheld.
All I can advise is that you contact your local SSA office for instructions on how to handle this issue.
Why did SSA refund the Part B? That doesn't sound right. Did you maybe get reimbursed for it on your retirement checks? My retirement reimburses me for it. Or were they taking out too much based on a prior year AGI? Then your income went down?