Phones not able to make/receive calls on WiFi calling. Renting XB7 router. Please help.

Please help. This has been going on for over a year and we just keep going in circles...a search on the forum shows that many others are having this issue but no solutions are posted. 

In our home with poor cell service  we rely heavily on Wi-Fi calling for work and personal use. 

When we home, and connected to wi-fi, we cannot receive calls. - they go directly to voice mail and we have missed out on critical messages from family members who we care for and needed help, as well as the emergency vet. We need a solution quickly. 

When we are home and connected to Wi-Fi, we cannot make a call. When we do, we get the error: "No response, Time Out" and "Mobile network is not available. Connect to a wireless network to make a call". The issue with the mobile network is expected b/c of the poor service in our home but we are already connected to a wireless network/Wi-Fi (and they are set to prioritize Wi-Fi over mobile).  It is as if the phones are not able to access the wi-fi network for calls (but they can browse internet). This occurs even if we are in the same room/next to the router. 

When we are home and connected to Wi-Fi, people call us and the call goes straight to voicemail. 

Often, texts are delayer can not be sent/received at all. These issues do not occur at our work (Wi-Fi) or when out in the community (cellular or store Wi-Fi).

The only way to reset the call/text services is to toggle on/off airplane more or restart the phone. This lasts only a few minutes before the issue reoccurs. 

This occurs on a few different phones (newer iphone, Pixel 8 and 9 pro, Pixel 4a, newer samsung, iphone 6). We have tested them all - they are all set for WiFi calling and connected to the XB7 router via our wifi/home network. The phones use either Verizon or AT&T lines. I've spent an exhaustive amount of time with Verizon and AT&T updating and resetting settings - including connecting directly to the router (not the mesh) and the local hotpot. We even did a full factory reset on 2 of the phones and it did not help. They continuously say this is an Xfinity/router issue. After reading the forums, I agree. There seem to be many with this issue but I do not see a solution. I hope people are being helped directly via xfinity and I just don't see the solution. 

It has gotten to the point that we upgraded our phones (from Pixel 4a to Pixel 9pro) and the issue continued. 

The only thing we can think of is that around the time we had issues we either upgraded our router to the XB7 or we upgraded the firmware on it.

How can we fix this issue?

We need this to work because we are missing critical calls and are paying for a service that is not working. 

Thank you in advance!