I have a Samsung Galaxy S8 and a SIM only contract with 3. This happens to be very good value and suits my needs. Until recently an app "3 in touch" allowed me to make calls (and texts) via wifi in places where network coverage is poor. 

Recently 3 withdrew the app, saying it was incompatible with their 5G upgrade plans. Since my phone is capable of calling over wifi I tried to enable it but the relevant setting is absent.

Since then 3 have consistently claimed that calling over wifi is only available if the phone was supplied by them. Which it wasn't. This is clearly nonsense and I have a complaint running via "Resolver" where they are still claiming this.

Can anyone here provide any insight please?