Hi, welcome to Three's users community.
If you have ported in today just wait few hours, I think it can take up to 24h to get all services ready.
Also might not switch to WiFi calls or even display it because the network signal strength is good enough to keep on cellular network. Have you tried: a) toggle off and on the WiFi calling option again? b) to switch on aeroplane mode and then switch on the WiFi only? (Don't forget to switch off aeroplane mode when you leave home).
Once the handset picks WiFi calling it will stick to it, but again depends on the coverage.
