the way it works is the origin account and the sims 3 account use the same email and password which then ties your code to that account but since you made an other account your getting the code is used message so you need to contact CS so they can assist with mergeing your accounts
to contact CS here's how
http://eahelp.ea.com/en/contact-us/new/
or
1. https://help.ea.com/contact-us
2.Set your language to US at the bottom
3.Describe your issue with a few words
4.Select Product: The Sims 3
5.Select Category: Billing/Purchasing or Account Management
6.Select Platform: PC
7.Click Find solution
8.Scroll down and click I still need help
9.Click Chat Now to chat with a Game Advisor
better still of you can find your code for the lost sims3 base game instructions are in the link I linked you can download the digital version of your lost one from your origin account if the games where registered , if you can't find the code then contact CS to see if they can assist with that (before considering going out and re buying the game that would be the last thing I would do after exploring the other avenues open to me i.e. trying to find the code myself then if I can't i'd then try CS after that if I cant get help with lost code I'd think about re buying )
before downloading your digital version you'll need to uninstall the disk version of that one game that is lost if you need a guide on which files to manually remove after uninstalling via the control panel let us know so we can post one for you
and here's an example of the games work
examples of how the games work the way the game's work you have the sims 3 base game then buy seasons you will play from the seasons expansion the base game will combine for playing then say you buy university the game will play from university (again the others combine for playing ) as that as it is your newest installed released game then say you buy an older released game like generations you will still play from the uni one as it is the newest released installed game you own and installed
if in the event you need to contact CS
1.https://help.ea.com/en/contact-us/
2.Click on the orange NEXT button
3.Select a platform
4.Click on the orange NEXT button
5.Select a topic and describe your problem in a few words
6.Click on the orange NEXT button
7.Click Chat Now to chat with a Game Advisor
guide on how to contact CS
http://answers.ea.com/t5/Beta-Archive/How-to-contact-a-Game-Advisor-using-the-new-EA-Help-page/td-p/2161281
