Email
[email protected] about the deleted character. They will email you back asking you questions about the account to prove that you own it. Some of the questions might be: what was the name of the character, what world, what was the account name, what other characters are on the account, what platinum items did you purchase with the character, and what items did you have in inventory. Try to answer their questions as best you can. If it's been a long time, there's no guarantee they can get it back. But they are wizards over at OTM, so there's a chance they might be able to. Good luck!
Edit: Also be patient about it. Only send one email. If you don't hear back from them right away, don't fret. They have a backlog of requests to work through but they will get to you eventually!