how do I delete my sims 3 account?

I think that you would be doing better with your problem by contacting EA's Help Center. 

http://help.ea.com/en/contact-us/new/?category=demo-beta

At the very least, the forum for either the Origin System or for the Sims 3's dedicated forum would have been a better option than "Other Games".

http://answers.ea.com/t5/Origin/bd-p/O-2

or

http://answers.ea.com/t5/The-Sims-3/bd-p/the-sims-3

Move to the sims 3 board

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Deleting your account will make you loose everything.

Change your password and then get in touch with a game advisor to have things sorted

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