Cruise Control problems of the 2008 Mazda Tribute

While driving on the interstate, I glanced down to see I was going 75mph. When I backed off the gas, the car did not slow down. It kept going to 75 mph even though I was not using cruise control. I managed to apply the breaks hard enough to slow the car down and get to the side of the road. (it took all my weight on the break to slow it down) I had the car towed where the dealer said the only thing they could find was that the rubber mat was wedged under the gas pedal. (I specifically remember sticking my foot under the pedal and lifting it upward in an attempt to stop the acceleration and slow the car. ) the mats are heavy duty and do not slide around or bunch up.