That happened to a guy I know when he moved from one state to another and applied for a a driver’s license. SSA had typed in the wrong line or initial or something. So he had to go to the local SSA office with his birth certificate and his license from the other state and they fixed it right then and there. He never found out what exactly had gone wrong, and it was odd that it didn’t turn off his bank account &c.
My FIL was dead for almost a year according to SSA ... it turned out the hospital had merged the files of two different guys with similar names. FIL survived and thrived but the other guy died. But we went round and round with our local offices. The problem went on until we called our Congressman. Once his staff got on the case it was solved in a couple of weeks. We were impressed.