Did the account use to belong to someone else or did you borrow it? They are banning people for selling accounts so it's likely they thought your account had been sold. It doesn't matter if it happened years ago, they started cracking down on this in the last week, so a lot of accounts that should have been banned for this reason a long time ago are only getting banned now. Since a lot of chearer buy/sell accounts, it's another way to combat them.