Registering game after downloading to computer

I bought The Sims 3 Deluxe from a local goodwill and have successfully downloaded it onto my computer, the issue is I can't figure out how to get it registered so I can buy expansion packs and whatnot onto my game. I've entered the code for both the game and the expansion pack into the EA app and Thesims3.com/register, but they're both telling me the codes have already been used. Is there a way I can get the game registered on the app or am I SOL? I was able to download the base game onto my computer and it runs fine, but I can't figure out how to get Sims 3 Ambitions on there without using the app. Any advice?