No phone number for incoming calls

I have an AT&T model CL82507 DECT 6.0 telephone system. Recently, the handsets stopped displaying the callers phone number, and instead displays UNKNOWN NUMBER. My service provider is Spectrum and when a call is received, the system always displays the correct caller’s name and phone number on my television.

Your customer support agent said the problem is probably in the telephone system, but I needed prove it. She suggested I borrow my neighbor’s system, which is identical to mine and see if it has the same issues. Initially, I thought that was a bad idea. However, I spoke to my neighbor and he declined for two reasons. First, he might miss calls from their multitude of doctors, and second, suppose my problem might adversely affect his system.