The Sims 3 Registration Code Invalid (Website) - Sister already redeemed code

So me and my sister share the same copy of the Sims 3. She registered her account on the website first and I'm not allowed to access it.

I wish to download from the Sims 3 Website however I need to register my game first. But because my sister already redeemed the code I can't register my game and thus I can't download anything from the website.

Thanks in advance.

Apologies if this is in the wrong place or something along those lines.