Mercedes Benz C Class my car will not go faster than 15mph

I have Mercedes c180 automatic, around 13 years old with about 70,000 miles. I owned the car for around 3 years and never had a problem until now. I was driving back home and braked to full stop in order to yield the way for upcoming car. Once the road was clear I pressed on gas but the car would not accelerate faster than 10 – 15 miles an hour. When I tried and pressed harder on gas it felt as if I was pressing on air. I turned the car off and restarted it again but the same situation would happen. I parked the car and went home. The second day I a mechanic came but the car this time would not even start. Another mechanic had no idea what is wrong with it. Another mechanic was quite convinced that it is a fuel pomp but he has had the car in the garage for a week now and everyday tells me that the he ordered the pump but they send him a wrong one and he is till waiting. I am afraid that he has not figured out what is wrong with the car and is embarrassed to tell me