Just wifi calling doesn t work???

Your cellular provider needs to offer it. I was on O2 and had iwifi calling., then moved to GiffGaff on the O2 network and lost it.

WiFI Calling is Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency who issued the SIM / eSIM to you.

Get help

1. Go to Settings > Phone > Wi-Fi Calling and make sure that Wi-Fi Calling is on.
2. Restart your iPhone.
3. Connect to a different Wi-Fi network. Not all Wi-Fi networks work with Wi-Fi Calling.
4. Turn Wi-Fi Calling off and then on again.
5. Go to Settings > General > Reset and tap Reset Network Settings.

Make a call with Wi-Fi Calling - Apple Support

There are two aspects to it, know it here

1. WiFi Calling --> Make a call with Wi-Fi Calling - Apple Support
2. WiFi Calling on other devices --> If your carrier supports Wi-Fi Calling on iCloud-connected devices, you can also make and receive Wi-Fi calls on other devices.