Possible call signal interference ONLY in the house?

Everything works fine almost everywhere (at work, at Xfinity store, on streets), except in my house.

As soon as I enter by house, I cannot play outbound or receive incoming calls from my iphone 11 with Xfinity.  There is no calling tone and after some time, it says call failed.  Calling from another phone (with a different provider) does not ring the Xfinity phone.  After some waiting and calling tone, it goes to voice mail.   I switched the SIM to another phone and get the same symptom.

What is puzzling is that if the call is started outside the house, it will continue just fine when I bring the phone inside, with no quality degradation.  Also, SMS works just fine.

I have had two tech support conversations, totalling ~2 hours.  Was asked to do multiple network RESETs on my phone, upgrade iOS version, and whatever.  Made two trips to Xfinity store, replaced SIM.  So far, no progress and no clear diagnose. 

The problem only started about 2-3 weeks ago.  Never had issue like this before.  Anyone ran into this problem?