calls go right to voicemail on iPhone 11 pro max

Usually the issue lies with the service provider. Do a manual network sync though the settings>mobile data>service provider options and click on the switch. Choose networks that are not compatible with your own, I usually do it about 3 times. The restart the phone. If not working then call your service provider for a network sync through their systems. If the last resort and the issue hasn't been resolved ask them to log a call to their technical support team or do a sim swop to a new sim if the sim is old.