Are you sure that you have the correct account name? From my own experience, changing serial keys does not prevent you from logging into your account. Its just that if you have a different serial key, you will need to put in your password correctly to accept the new serial key once you log onto the character. Otherwise your character will be frozen.
This is based on my experience of playing on the same account from different devices (mobile, ipad, pc). So you may not need a DM for this. However if you can’t get as far as seeing the character selection screen, I am guessing that you are using the wrong account name.