Have you tried logging in, navigating to the Datacenter where your Character is currently residing, right click on the Character in the selection menu, then selecting "Return to Home World".

It shouldn't allow you to purchase a Name Change to begin with, as:

"Your character must be on their Home World to perform name changes, so please be sure to log out from your Home World before using the Character Renaming Service."

But alas, this is basically a bug since you are now locked out of using said Character.