Accidentally overwrote someone else's game with mine, lost my items and SimCash

Best thing would be to contact an EA game advisor about this issue.
You can do that through this link: https://help.ea.com/en/contact-us/
If you want to do so in a different language you can choose your country of choice in the upper right-hand corner. 

You can also choose to contact an EA game advisor through social media:
- Twitter: https://twitter.com/EAHelp
- Facebook: https://www.facebook.com/EAHelpHub/