I have a Samsung S10 (SM-G973U) which I use with Smarty mobile in the UK, which uses the 3 network. Recently (the last week or so) the 3 network has been undergoing some maintenance in our area and I haven't been able to make or receive phone calls. I have tried to enable wifi calling but the option does not seem to exist under call settings where it is supposed to be (see attached screenshot). 

My wife is on the same network (Smarty) but has a Samsung S20, and she can use wifi calling no problem, and the option to turn it on and off is there is call settings whet it is supposed to be. 

Does anyone know why my S10 doesn't have the wifi calling option? My phone says under call settings that the latest version is installed and there are no updates outstanding.

Thank you,

Matt