Can not receive missed calls on whatsapp

Hi, I have a Samsung Galaxy S4 and for the longest time I would receive calls and wouldn't even know it. I would get no missed call notification, my phone wont even ring. But I can make calls and when im in one none of the buttons work either. I cant mute or go on speaker phone or message or even end the call. Somtimes the call even makes the screen go black and I cant even go back to the call screen but i can still stay in the call. Does anyone know how to fix this? Thank you for your help