Automatic Emergency Braking problems of the 2020 Chevrolet Blazer

I backed my vehicle out of the garage and put it in park and stepped out of the driver's door. I was going to put my son in his car seat in the rear seat when the vehicle started moving backwards and the opened driver's door knocked us down. I was able to push my son out of the way, but the vehicle continued and the front left tire rolled over both of my legs. The vehicle continued in reverse along the driveway, struck a trash container and went up the incline at the main road. It crossed a busy two lane road and into my neighbors yard. The vehicle came to a stop about 10 feet from our neighbor's house without striking anything else. We purchased this car used with just under 300 mile on it. During the time that we've owned it, it has randomly flashed a "shift to park" warning lamp on the dash when I shift it to park and turn it off. It has never done what happened to me today. A few months ago, my husband and I took the car to the gm dealership to have it checked out before the warranty expired. We told them about the "shift to park" warning lamp and that the car was shifting hard while driving it. They kept the car a few days and told us they were unable to find anything wrong with it.