Did you try it without this handset in another phone?
I have been running into an issue where I am not receiving some calls at all. I had people tell me they called me, but my phone hadn't rang and I had zero missed call notifications.
It is damaging my image in a bad way.
I am using Mi 4i handset
Airtel post paid SIM (earlier was using Idea. Same problem was there)
Please help me to get it solved.