Medicare is mailing new Medicare cards starting in April. The new cards will have a new, unique Medicare Number instead of a Social Security Number. Make sure… your mailing address is up-to-date. If you need to update your address, visit https://ssa.gov/myaccount or 1-800-772-1213. TTY users can call 1-800-325-0778. If you are a Railroad retiree, contact the Railroad Retirement Board at 877-772-5772.