Brake Grinding Noise problems of the 2014 Chrysler Town & Country

I got into the car which had been parked on a hill. The front of the vehicle faced upward. I turned on the engine and put my foot on the brake. (at that moment I didn't notice that the brake was stiff). I switched gears into drive and it slowly slid backward down the hill. My foot was on the brake the entire time. I pressed harder without any reaction from the brakes other that a grinding noise. The car did not slow down but gained momentum as it rolled down the hill and crashed into a parked car. Due to the fact that it was a slow motion accident, I had time in which I double checked that there was nothing under the brake and that I was indeed pressing the brake and not the gas. I have a dashcam video if you need. My husband was able to duplicate the problem: whenever the car is cold and on a steep hill with the front of the car facing upward, the brakes stiffen up as if the engine is off and you pump the brake and it is hard. I have notified Chrysler who is opening an investigation. I so far haven't heard back from them.