W221 will not move

Hi i have a w221 s class 320cdi  that was all working fine and then all of a sudden has developed a fault it starts but will not move i have tried all the different modes as in comfort sport and manual but it just will not move. The engine revs up when i put my foot on the accelerator but nothing else. I have sent it into the garage but they can not tell me for defiantly what is wrong with it. It did have two fault codes but i stupidly deleted them thinking it mite work and it was just a glitch. Unfortunately i did not take photos and can not remember what they where. It did have an issue about a week before it stopped moving and i did take photos of the fault codes that i have given to the garage. They recommended i get the transmission refurbished. I'm not sure what course of action to take next.... getting the transmission refurbished is very expensive and if they are not 100% sure it's that i could be out of pocket and still transport. They still have the car and have done a transmission service which has made no difference. Any advise would be greatly appreciated.