In order to redeem the code follow the instruction below:

Go to http://www.thesims3.com and make an account if you do not already have one. If you already have an account, skip to step 2. If you already have an Origin account, please use the same email and password to register on http://www.thesims3.com.
Once you are a registered member of http://www.thesims3.com, login to your account so that you can then register your game codes.
Click on the My Page tab.
Then click the My Account tab.
Click on Register a Game or use this direct link: click here
Enter the product code for the expansion pack or stuff pack.
Click the green Register button.

If the method above won't work, please follow the instructions below:
 




Go to: http://www.origin.com/us/about
Click "Download Origin" (from the upper left corner)
Download Origin 

Login into downloaded application
Install and start application, login with your Account name and Password
(create one here: http://store.origin.com/ if you don't have).


Reedem Product Code
From the "Origin" drop-down menu (upper left corner) choose "Redeem Product Code...",
enter your code and click "Next".


Download your Game
After successful code verification go to the "MY GAMES" tab and start downloading.