Began Medicare December 2022, Social Security January 2023. Was billed in November $510.30 by CMS for premiums, which I paid. Now I have received letter stating $324.60 is being deducted for past-due premiums plus $164.90 for medical premiums from this payment. What do I do?

Hi. You shouldn't need to do anything. You can't prevent the Part B premiums from being deducted from your Social Security benefits, but any premium overpayment should automatically be refunded to you. In my experience such premium overpayments were normally refunded within 60 days, but some people have recently reported waiting longer than 60 days for their refund.

Best, Jerry