If, on the other hand, you bought the disc used, then it's possible that the original owner already registered the code. It would be useful to have proof of ownership-in your case, photos of the disc, case, and insert with the code-on hand for the chat.
If you can't figure out what email account you used back then, you'll need to contact EA customer support to get it sorted out. If you get a message stating that the code has already been registered, it's possible you added it to your account a long time ago. The two share information, so the game will be added to your account in both.
The same product code on the back of the insert in your CD case will allow you to add TS3 to your Origin account, or you can create an account at the Sims 3 store () and register the code there.
