I once had to drive my boss's car which had an after market cruise control. Heading south on Interstate 75 with the control set for 70 MPH (the legal limit) I became aware that the cruise control became unresponsive to user commands. Hitting the brakes did not disengage it. Pressing the power switch had no effect and neither did any of the other cruise control switches. I had very few options left to me to maintain control of the vehicle which continued going 70 MPH or would try to when I hit the brakes. It seemed the only way to override the unit was to kill the ignition, something I was not going to do on the expressway. Switching the ignition off would lock the steering column. Shifting into neutral would destroy the engine. What I finally did was maneuver into a long exit lane and brought the vehicle to a stop with the brakes while the engine did its best to maintain 70. Once I got the vehicle stopped I did kill the ignition, took a few deep breathes and restarted the engine. It started normally and ran at idle speed. I kept the cruise control turned off and finished the trip, and told my boss about his piece of crap cruise control!

As to the OP's cruise control, I would not want a car that had it within a thousand miles of me!!!