Cruise Control problems of the 2006 Hyundai Azera

While driving in la, CA with speed control set at 65mph I was making a lane change. To allow more room between myself and the following car I accelerated by stepping on the gas pedal. The car speed increased and I removed my foot from the accelerator to return to the set speed. The car did not slow down. I stepped on the brake to #1 take the car off cruise control and #2. To slow down. The car did not slow down and I was now moving at about 80mph. I stepped with my left foot on the brake pedal and tapped the gas pedal. Still the car did not slow down and I had difficulty keeping the speed down by applying the brake. I shut off the ignition and as I was in the fast lane (left) I moved off the lane to bring the car to a stop. This happened three more times while driving in la. On 02/03/14 while driving on i15 I wanted to see if I could duplicate the condition. Again the accelerator got stuck and I had to shut off the motor. I brought the car to the local Hyundai dealer who reported that they could not find anything wrong. As the same thing happened while driving home, I went back to the dealer and on a test drive with a technician the accelerator got stuck again. I need your help and assistance in this matter which is a serious safety issue.