android keep screen on while on call on Android 8.0.0

I guess I have a problem with the proximity sensor. The screen turns off when I start a call but it's impossible to turn it on again. The only option left is to hard restart the phone. I'm using right know the power button to ends call. Still, it's impossible to manage voice messages (delete or save them) or to interact with any other automated call. I'm not able to find settings for incoming calls as other posts mention and apps such as Screen On do not seem to work. Any idea of how to keep screen on while on call on Android 8.0.0? Maybe using a particular call app? Best, Rafael