VPN blocks calls on iphone

We seem to be having an issue with our iphones and wifi calls being blocked while using the Avast VPN and using wifi calling. Our ISP is Xfinity/Comcast. Is there a way around this issue to allow us to use a VPN with Xfinity/Comcast? Our cell phone provider is Verizon. On my phone, I have to go to settings and turn VPN off, then go to General-VPN & Device Management, click on VPN, then make sure it’s not connected. The Device VPN is Avast Web Protection. I’ve gone to that and deselected Connect On Demand.