VoLTE has to be supported by network... Your profile on HSS and IMS should be having this service... Meaning that your network provider has to subscribe you to this service. Unfortunately most of the customer care people don't know difference between VoLTE call and internet call.
Hi dear, insert an Indian sim other than JIO and reset your phone. When reset is completed and phone turns on there will be a message on screen which says DEFAULT SIM CARD HAS BEEN CHANGED. It will ask you whether you want to set up your device with new sim card. Press yes. Device will reset and restart automatically. Now check whether Jio is working.