WiFi calling does not work properly

Two Issues: 1. When I answer a call when WiFi is on the call is immediately dropped.

2. My iphone7 randomly switches between Xfinity mobile signal and WiFi...no rhyme or reason for it.

I have Xfinity for my Internet service and my cell service. I've been a technologist for over 40 years.  I've repaired everything from aircraft instrucments to computer systems.   This appears to be a software issue somewhere on the Xfinity side.

When I call Xfinity I get low end representatives that have no idea what they are saying.  One said she would put in a call report so I would get to a higher level person...she never did it.  The next one tried to tell me that I had to turn off my internet service, select WiFi on the phone and then turn the internet service back on.  When I told her that doesn't make any sense she switched her tune and said it was an Apple problem so call them.  I said no I want to talk to someone of authority.  She said a supervisor will call within 24 hours.  I'm not going to hold my breathe on that one.

The Xfinity customer care for iphones is really terrible.  I have an iPhone 7 plus.  Has anyone figured out a solution?