Can't dial out on landline.

I have a dial tone on my AT&T landline phone, but then no ringing, only silence or sometimes squealing. There is an error message on all three handsets: "No Home Line."

An AT&T technician had me plug in a second phone which also did not work.  He said that showed that nothing was wrong with the phone and that I should contact Xfinity about the service.

I tried to reach a real agent, but was kept out by a firewall of automated phone trees and virtual agents.  I was told to restart my router about four times. They kept referring me to articles about what to do if you have no dial phone. I tried to explain that my dial tone was fine, but he virtual agent said it couldn't understand my conversation unless I pressed one of the following buttons. ,

Troubleshooting              Manage my account            Review Latest Bill            Make a Payment

When I pressed Troubleshooting, it gave me some more articles about no dial tone.

I gave up after 2 hours and tried to schedule an appointment.  But was told that I can't schedule an appointment without going through the virtual agent.  But the virtual agent kept telling me that it could solve most problems without an appointment and kept giving me articles about no dial tone.