Problem

I tried to register my game on thesims3.com but I get the message that my code is already used/invalid
Origin ask me to activate my game but when I try, it tells me my code is used/invalid

Cause

Your game is automatically registered on thesims3.com if your accounts are connected.
You only need to activate your game once. After that you should the game on myGames on the Origin client.

0, D and O and 8 and B and 2 and Z look very similar. Make sure you did not mix them up.

If you activated the game on Origin, there is nothing more you need to do. The games should appear in myGames on the Origin client. Log out and back in on thesims3.com to make the icons show up there.
You should get a extra email for your limited edition contents. Here’s instructions how to redeem them: How to redeem the limited edition content
If these solutions don’t help and the games don’t appear in myGames on the Origin client or on your myPage, you need to contact customer support.

If you are sure that you have entered the code correctly, get in touch with customer support or try to exchange your disc at the place where you bought it.