Why can't I register my account with the Sims 3 Community?

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If so, I would contact a game advisor 

Game advisors can be found through live chat.

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
   

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