general problems of the 2005 Mercedes Benz S500

Took my car to mercedes-benz of pembroke, pines florida I took my car to the dealer last mo mercedes-benz of pembroke pines florida for them to change the oil and filter in transmission. So, Monday I took it back in and told them to check my key door locks, because the door would open. "no key" but would not lock by holding the handle. Also, to check the transmission which was harsh when down shifting when it was cold. I got a call the next day telling me I needed a new transmission. I said I only have 52,000 miles on the car and I don't use it that much. The car cost $93,000. 00 this should not be. Something is wrong at that dealer, and they won't listen to me, the service mgr won't even return my call long story short, but the bill was $9,300. 00 I think I got ripped off. Thank you.