Customer service cannot assist with beta access, but you can sign up for individual game betas on the game website when the beta signup is available
Information on Call of Duty: Modern Warfare III Beta Access
Your Battle.net account does not have access to this beta content.
How to receive access to Alpha or Beta testing.
Information about what to do if you are experiencing reduced performance on the Beta version of the Battle.net Desktop App
Troubleshooting steps for the Battle.net desktop app getting stuck on Starting...
Addressing issues when Battle.net Application is stuck on Downloading New Files when launching or installing.
You need to patch the Battle.net desktop app in order to uninstall.