lanchus7 If you registered your disc on the old Sims 3 site (www.thesims3.com or store.thesims3.com), that's why it's showing as used now: that site and the EA App draw from the same database. But that means you could simply login with whatever email address you used at the time, and the content should already be in your EA App game library.
If you can't figure out the email address you used back then, contact EA customer support to ask what happened to your code. A support rep may be able to find a record of your registering it. It's also worth signing into ea.com with any email address you had at the time (click "Forgot your password?" to get a password-recovery email) and seeing whether you can find a corresponding entry under Account Settings > Order History.
I would strongly suggest using the live chat option rather than email. If you don't see it, try this link:
https://help.ea.com/en/help-contact-us/?product=the-sims-3&topic=missing-game&category=manage-my-account&subcategory=find-missing-game
Make sure you're signed into an EA site (this one is fine) before clicking the link and that the location in the lower-right corner of the browser window is set to U.S. or U.K.
Alternately, try using the help site without being signed in. Some categories of issue allow you to proceed without an active login, and many of those offer the live chat option.
