Unable to END phone calls on 4S
My iPhone 4S, iOS 8.3, has lost the ability to end a phone call. When I try to hit the "end call" button the screen goes black. I try to end the call by pressing in the area of the "end call" button but it doesn't work. The only way I can see that I'm still on the phone is when I press the home button, but I am still unable to hang up! I have turned it completely off and then on again with no different results. Please help me!
iPhone 4S, iOS 8.2