My email was used as an alternate on someone elses account and I can’t remove it.

I received an email today saying that information for my alternate account had been changed but the account is not mine. Some how, my email was added as an alternate email on someone elses account. This allowed me to go into their account. I tried to remove my account but it wouldn't let me without an alternate email to replace it with. I tried to close the account but it says it will just reactivate if it is logged into again in the next 60 days so I just changed the password on the other account and on mine. I don't know what to do! I don't think this will work because if I could change the password on their account to be able to log in then can't they do the same to mine? Please help! And might I add that it is ridiculous that you do not have a support telephone number! This is an issue that really can't wait to be resolved. I have personal information in this account and it is not something I can fix!