I have been paying 2 Medicare premiums for 15 years. How can I get my money back

Hi. I don't know how that could happen, but if you did in fact pay duplicate Medicare premiums then the overage should have been automatically refunded to you. If you paid the duplicate premiums out of pocket, then you'd need to contact Medicare (https://www.medicare.gov/forms-help-other-resources/contact-medicare). If the duplicate premiums were withheld from your Social Security benefits, then you'll need to contact Social Security at 800-772-1213.

Best, Jerry