WiFi calling not working

[Musgrave]

I've an iPhone 16 Pro running iOS 18.6.2 with Three 64.2 and WiFi calling doesn't work on my Community Fibre internet. I cannot make or receive calls. As soon as I disconnect WiFi it works. 
Anyone else? Is this a Three issue or a Community Fibre issue?

[Billy-Bob]

I'm on Plusnet FTC with the same iphone 6s for years.

WiFi calling stopped working last week and Three seem to have no idea why.
Wifi calling works with the same phone and WiFi connection when using Labara.

I'm getting more than a little irritated by this.