Vehicle Speed Control Related Problems of the 2021 Subaru Legacy

Vehicle Speed Control problem

After shifting my car into reverse, I slowly started removing my foot from the brake pedal. At this time, the car started rapidly accelerating backwards so I put pressure back on the brake pedal to stop the car. When doing so, the abs light came on my dashboard, I heard a griding sound like the car was still trying to accelerate, and there was a loud constant beep. I was able to shift the car into neutral and then into park to stop the car and then turned the car off. I contacted the dealership about the issue, but have not yet been able to further investigate or bring it into the dealership.