It’s possible that number has been recycled by the carrier or that someone accidentally entered your phone number when they registered for their account.

The easiest thing to do is to is:

AT&T, Cellular One, Sprint, and T-Mobile users text “reset pw” from your phone to 69937 (MYXER) and we’ll send your new password to your phone. (All other users please text “reset pw” from your phone to 9543046522)

Once you sign into the account, just go to the Account page and update the email address on the account.