I re-input my code and it said the code isn't valid because it's been used already.

I then tried to log in to Lodestone and I got this message:

Use of the Lodestone requires a FINAL FANTASY XIV service account with at least one character.
Please log-in again after you have created a character in-game.

I'm now pretty goddamn angry. I paid for this game, and not only is it telling me I haven't registered, but I also now (according to Lodestone) have no characters.