I have been using my XZP for more than 16 months. There was no problem with the VoLTE feature until a few days ago the VoLTE logo disappeared, when calls are made, it drops to 3G connection. When I change to my wife's SIM card which uses the same service provider, the VoLTE is active again. When my SIM card is put into her mobile phone, VoLTE is also active. This makes me puzzled and I cannot figure out what is going wrong. I went and called the technical support of the service provider, they said that there was no problem with my service and VoLTE should be enabled. Are there anyone who have encountered similar problems to mine?
P.S. My service provider is Hong Kong CSL. I have changed to a new SIM card and the problem persists. A factory reset to the mobile phone also doesn't help.
