how to redeem product code

Hi i got the sims 3 game for christmas,i installed it and didnt take any notice that i had installed origin then it said i needed to make a new account in order to play sims 3 so i made one and i didnt think i would need my password so i didnt write it down, i tried and tried to get my password but it would let me ;(

so i decided to make a new account so i could play the sims so i did and then my account asked for a product code of the game i wanted to play which was sims 3 ,i entered to code on my game case but it said my product code had already been used ? soo i kept on trying to remeber my password for my account but i cant and i really wanna play my new game coz i go generations axpansion pack and pets pack ☹️ which is a real bummer ,so can anybody help me out coz im in desperate need of sims to play

Thanx,

olivianorthway