You need to boot your phone into safe mode to determine if there's a malicious third-party app causing your problem. Go to this Samsung website and follow the instructions there to enable safe mode and identify the likely cause of your problem: https://www.samsung.com/us/support/answer/ANS10003495/
I recently had an issue like that and before I really found out what was happening my screen stopped working. It was so random and while i was using it. And it would also randomly answer calls for me.
