Your home or neighborhood must not have a strong Verizon tower signal? Do you have any neighbors on Verizon? They would have the same issue.
Turn on WiFi Calling under your cellular settings. Be sure to add your address exactly as shown on your Xfinity account. This will automatically route your cellular calls and texts through your router/modem/Internet to the XM/Verizon cellular servers when your cellular tower signal is poor or very congested.