iPhone X freezes at end of call

Hello there,

I know this question has been asked before but there are no recent answers so I was advised to start a new topic on this.

I have my iPhone X since a month now and every time a get a call (or call someone) I can't end the call. This occurs both with 'normal' telephone calls as well as with WhatsApp-calls. The screen is black and none of the buttons work. Updates to newer OS didn't help.

Sometimes, after 1-20 seconds, the screen comes back but sometimes the only thing that helps is to shut of the iPhone (pressing the buttons very long until it gives me the option to shut off the device).

Can somebody help me?