No WiFi Calling Option

[fopetesl]

I have a PAYG 3 SIM because it's the only provider that works through EE here in North Yorkshire. And it's cheap
However 3 have decided to drop three-in-touch as from 15th, next. Advise to use phone's WiFi calling option.
Problem. I have no WiFi calling option either on Phone->Settings or Apps->Phone/Wifi/Additional Settings.

Spent all morning downloading, installing and checking firmware is up to date.
The phone works fine on mobile and WiFi apps, Whatsapp, Three-in-Touch, etc.

I 'chatted' with Samsung who insist that it is up to 3 to enable WiFi calling.

3 support insist it is not up to them only with Samsung firmware 'upgrade'.
Suggest I try my SIM in a WiFi enabled phone.

Samsung insist there is no other firmware upgrades.

If I cannot fix I essentially have a brick outside of 3 coverage.

 

[Rukbat]

How old a phone are we talking about? How old a version of Android? Is the phone carrier-branded or not?

 

[fopetesl]

Don't know the actual age. It's a Galaxy S6 Edge SM-G925W8 so about four years, I guess.
Android 7.0, Kernel 3.10.61-13731302
SIM free, tested with 3 & EE

 

[Ron MacRae]

I've got the same problem with an HTC U11+ with Android 8. No Wifi calling option. If three remove their in Touch app my phone becomes a brick as I've got no signal from any provider where I live.

I tried to update the software but it told me there were no updates.

 

[fopetesl]

Anyone. Ideas, please.
That's two of us, me & @Ron. There will be more.