[Sims 3 Console] Please post here

So I bought a xbox 360 version of the sims 3 from a gamestop store a little while back, and it does not have a serial code or anything. So for registration, and linking, I'm screwed ain't I? Every time I start it up, it asks for acces code. I enter the only code I can find on the thing, and it's not long enough, it needs a 20 digit code. So I have no idea how or where can I get one or retrieve it. I really would like to so I don't have to struggle with having to go through it every time it starts up. Can anyone help. It's xbox 360 The Sims 3 a platinum hits