if you bought the game second hand chances are the previous owner regestired the code to their account and is tied to tha account
if you regestired your game in origin first then you do not ned to rereg it on the sims 3 account if you used two different emails and passwords for both accounts you'll need to contact CS to assist with mergeing the accounts
FAQ http://answers.ea.com/t5/The-Sims-3/FAQ-Invalid-and-Used-Serial-Codes-amp-Games-not-showing-up-in/m-...
if in the event you need to contact CS
http://eahelp.ea.com/en/contact-us/new/
if you live outsude the US try change at the top of the page the flag to US
1. click on the blue link
2.choose your product in the search menu after that click on next
3 select your platform pc, android , wii...etc click next
4 choose topic in the search menu for example billing/purchase then in the menu that apperars under that type in something about the issue for example overcharge click next
5 click the orange live chat to chat with an advisor
