Serial Code Invalid

I have all of my expansion packs for the sims 3 installed into origin but for some reason sims 3 generations will not connect to origin.  I bought and downloaded it from amazon onto my computer.  When I try to redeem the code on origin it says that the code has already been used but the only time I used it was when it was downloading to my computer which i did with every other expansion pack when i bought them as well.  I just want this game to be included on my origin with everything else in case something happens to my computer.  if necessary i can send you the code i am using and a screenshot of my game library on amazon to prove that i purchased the game.  please help me !!