My IPhone 5 won't hang up phone calls using the end button on the screen
I Have a IPhone 5 in fact my second new phone. The first one would not hang up phone calls using the end button on the screen. I took it into an apple store and talked with a person at the Genius Bar. They had no idea what the problem was and had never heard of it. Based on what I have read on various forums I don't believe that to be true. They gave me a new phone and it worked properly for about a week. Then it started all over again. When it is connected via Bluetooth to any of my vehicles the button on the screen works just fine. The only way I can end a call on the screen is to put it on speaker and hit the mute button and then the end call button will work. Everything else on the bottom of the screen works fine, that to me would indicate the sensors are working. Is this a software issue. HELP
iPhone 5, iOS 6.0.1