Horn Assembly problems of the 2004 Audi A4

I owe a 2004 Audi A4 convertible. In late February of 06, I started to experience problems when I put the gear on d (drive) or r (reverse) and gave gas; the car did not move at all. Dash board instrument was not responsive either. Initially I thought this was due to cold weather. On March 13, 06, I was running errands in a very busy area of northern virginia. The car was warm as it has been running for a couple of hours. I approached a busy intersection to make a left turn. When the road was cleared, I attempted to move forward but the car was totally frozen - it would not move regardless of how much I pushed the gas pedal. I was now facing the oncoming traffic of three cars blowing their horns like crazy. I just could not move the car and was terrified that I would be hit by the oncoming traffic. The oncoming traffic came to an abrupt stop and after several attempts I was able to move the car. I was very scared and called the Audi of tysons corner (hbl) in vienna, virginia immediately and took the car in that day. The next day (3/14) afternoon, I received a call from the service advisor indicating that they were not able to duplicate the problem and that nothing was wrong with my car. I insisted that they recheck as I experienced the problem several times and that the last incident was could have been fatal as I was stuck in the middle of the intersection. They agreed and kept the car for another day; however, the next day they called and said the same thing - nothing wrong with the car. I picked the car on March 16, 06. While waiting in the lobby, I saw another Audi A4 convertible driver. I approached her about my experience and asked if she experienced the same or similar problems. She said yes and that is why she brought her car in along with a regular service check. She received the same feedback from the Audi of tysons - nothing wrong with her car either. I have the name, phone number, etc. , of the other driver if needed.