Why my galaxy tab 3 (sm-t116nu) locks itself immediately during a call?

[AC Question]

Hi, I have a Samsung Galaxy Tablet 3 (SM-T116NU), it locks itself immediatelly everytime I make call. What can I do to remove this? It needs unlocking everytime I want to recall. It is disturbing, please help me!
Kuchibanda

 

[Rukbat]

It sounds like a defective proximity sensor, or you have a case or screen protector blocking it, making the phone think it's next to your face even when it isn't.