I am using Jio and VI SIM's, and Airtel Fiber as a Wifi. I think my issue got resolved after One UI 6 and 2-3 restarts. From last 2 days, i didn't received any complaints regarding incoming calls. Hope it's fixed.

Which SIM's are you using? Do you have wifi connection?

Reseted network settings many times, reseted phone to factory settings many times. Visited service center thrice. First they said to update sim, later installed os, then they said they done binary update. Nothing works.

Check this out.

Already using lte, not working.