Why does my screen lock during calls?

[Windows Central Question]

Have had my lumia for 4 weeks now, in the past week everytime I make a call the screen goes blank as soon as I hit the call button. The call still goes ahead but I can't access the screen until the other person hangs up. This means I can't hang up or access the numbers during the call????? I can push the on/off button and the screen will flash up for a millisec but then its blank again????? Any ideas????

 

[srikanth reddy4]

the proximity sensor is not working properly....take it to the nokia care