Windows Phone 8 screen stops working during phone call

[MEKHALA]

I dont know what went wrong with my new Lumia 620. I am having this phone since a month now and it was working fine. From last 5 to 6 six days whenever i make or receive calls, i just cannot operate my phone during the call. My screen stops responding completely. I know the touch screen technology disables the screen when we put the phone on ears because of the sensor, but my problem remains even if the phone is on loudspeaker. I guess the touch should work in this situation, right? Mine doesn't works.

Any suggestion what would have gone wrong? The problem started recently, it wasn't earlier. Any help would be appreciated.

[Caiden]

whenever i make or receive calls, i just cannot operate my phone during the call. My screen stops responding completely.

Did you tried restoring the phone? Factory reset?