When I make a call, the screen goes DARK automatic even after keeping phone in my hand. Why???

[Windows Central Question]

I know that the proximity sensor is there which automatically black out the screen we take our phone nearby to our ear. But I am facing problem just (time tends to ZERO) after making the call. Also when I try to add another call for conference, it does not responds.
Kindly suggest ...

 

[hotphil]

What phone?

 

[ratsttam]

Do you by chance have something covering the upper part of the screen? Like a screen protector that doesn't have cutouts for the camera and other sensors at the top.