Account Problems

Awhile ago, I created a EA account on the official site. I lost the information on that one and I am not so sure if it was saved on my xbox. So recently I created a new one and I am trying to get the CE & Terminus gear codes working, but since I assume my old account is on the same xbox or hard drive (I also got a new xbox and hard drive) I have no idea of knowing whether or not I am able to change it. On the social bioware I put in my recent EA account information and I assumed it would automatically verify my gamertag on xbox. But that didn't happen, I've spent hours figuring out how to configure the new account to my xbox and the gamertag. I do not want to lose both DLC's. I have also registered the game (if that matters). I need someone to answer these questions for me ASAP. I am quite new at this sort of stuff. THANK YOU!