What can I do if my operator won't let me use VoLTE and VoWiFi on my Mix 4 specifically? I know that it works perfectly on my Mix 4 in France on Orange network (not my actual operator, I'm on a MVNO) because I have used it when I put my SIM card in it in the first place.
I had an idea : I switched my SIM to my """old""" Mi 10T Pro (original EEA rom), got back my VoLTE and VoWiFi (IMS registration) after ~12 hours, then put my SIM card back in my Mi 4 and after ~3 hours, VoLTE and VoWiFi gone. They won't come back until I put my sim card in another phone and wait for these services to come back...
I thought that maybe they could "validate" my IMEI to use these services but idk if the problem is here