Sorry for the trouble caused to you! The screen-on/off function during calls is activated by detecting the proximity of the face to the screen. If the ear's contact area during a call is too small or if the distance to the face is too great, it will not be detected, resulting in the screen not turning off. If the power button is accidentally touched during a call, the screen won't automatically turn on when your face moves away from the screen. In this case, you can press the power button to turn it on.
Additionally, unofficial protective films will affect the screen's on/off function. You can use official protective films or try to tear off the existing films to solve this problem. This is not a product quality issue. Please feel assured to use the phone normally during calls with proper posture.