WiFi calling not working

[Lobster]

Hi, I have an iPhone 12 under a plan with WiFi calling enabled on the device and super strong WiFi network at home, however, when I test WiFi calling by activating airplane mode and turning the WiFi on and trying to make a call, the phone tells me I have no network connection, which I do because I use my network all day long for data. What could be causing this problem? NB I have WiFi and 4G calling showing as activated on “my O2” also. 

[MI5]

@Lobster 

Sounds like it's not enabled on your account.

You'll need to call customer service.
Numbers here Guide: Coronavirus Community Help and Support 
When it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Say "Upgrade", "Lost/Stolen" or "Fraud" if you have to, to get put through to someone.
8.00am is the best time to call if you can.

Also check with them that iData is enabled.

[Lobster]

Thanks, spoke to O2 and went through their trouble-shooting (basically checking for the obvious). Apparently all iPhones are eligible by default for WiFi-calling so no action needed to my account. The last thing they wanted me to do was take the SIM out and “give it a wipe”, that unsurprisingly did not work either. The phone just seems unable to pass VOIP calls via my network and so they have escalated this to technical support.