My sims 3 pets code says its used

if the game was/is second hand /used unfortunally with second hand/used games   if the original owner registered the game to their account the code is tied to that account codes are non transferable nor can they be reregistered to another account

also see if you use the redeem a code in your origin 

if for a new game see the FAQ http://answers.ea.com/t5/The-Sims-3/FAQ-Invalid-and-Used-Serial-Codes-amp-Games-not-showing-up-in/td...

if the game is new and you still have issues after reading the FAQ and it does not help  if you need to contact CS here's how

if in the event you need to contact CS

1.https://help.ea.com/en/contact-us/
2.Click on the orange NEXT button
3.Select a platform
4.Click on the orange NEXT button
5.Select a topic and describe your problem in a few words
6.Click on the orange NEXT button
7.Click Chat Now to chat with a Game Advisor


guide on how to contact CS

http://answers.ea.com/t5/Beta-Archive/How-to-contact-a-Game-Advisor-using-the-new-EA-Help-page/td-p/2161281