My screen won't turn off during a call

Hey guys,
i have a problem with (i guess) a proximity sensor setting or something?

when i make a call, and place the phone to my ear, the screen won't turn off \ go black.

Someone knows how to resolve this?

I've tried calibrating and cleaning the proximity sensor, that didnt work.
i think the sensor itself is fine, because it does auto rotates the screen when i rotate the phone

Thanks