If I Bought Sims Online How To I Register I Just Bought Brand New Sims Online For My PC & When I Install It States The Reg. Number Already Registered?

I just bought brand new Sims Online for my PC & when I install it states the reg. number already registered? - if i bought sims online how to i register

When you reach the registration code, states that have already been registered. This is a brand new game. How do I solve this problem?