Change your password.
Remove all authorized users
Add the unique 4 digit PIN number/extra security and don't give it out.
Go paperless and pay online.
All carriers provide these security measures. If we maintain them the account cannot be hacked.
If your account has been compromised already, you may need to take additional steps, like changing your email, and put 2 step verification on your email.
It is each persons job to use the security available to them. If you leave the proverbial door unlocked, and don't set the alarm, you can't blame the police when you get robbed.