Not receiving Calls

I gave my son my iPhone 7 Plus when I upgraded to my new phone. He has his own cell number. His phone worked perfectly for a year now.

All of the sudden he is unable to send/receive phone calls, send/receive FaceTime calls, and Siri doesn’t work.

I’ve checked the do not disturb feature, I’ve rebooted the phone and even took the SIM card out and put back. He’s able to use the internet, apps, and games. His cellphone service still works when he doesn’t have WiFi. He’s able to watch YouTube and whatever else that needs a cellphone service to use.

currently running software version 13. I don’t see any damage to the phone.

Any Help on this matter would be greatly appreciated!!!!!

Thank You,

Phil