The Sims 4 for Mac - Redeem Code Already Used

Are you sure you logged in with the correct account ?  Use your email address instead of username.

Log out completely, turn off Origin and restart it. Then try logging in again. If that doesn't work either, reinstall Origin

Also make sure your games are not hidden and games and platforms is set to all.

Here's two threads with further tips

• http://answers.ea.com/t5/Origin/I-bought-a-game-but-it-does-not-show-up-in-Origin/td-p/53928/
• http://help.ea.com/uk/article/origin-my-games-list-is-blank

If all fails, please contact a game advisor

Game advisors can be found through live chat or call-back

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 or leave your phone number for a call-back
   

In Details here: How to contact a Game Advisor using the new EA Help page