Best answer by Mohammed
Are you on the latest version of the software?
When you say it's not working, do you mean that it's never connecting to WiFi Calling at all regardless of if you have no service?
Usually, WiFi calling kicks in when you drop down to below a set signal, it won't always be on by default.
Have you tried putting your phone in flight mode and then turning ON WiFi and seeing if WiFi Calling connects?