front rotors on my 124 were 35 each pads 15 for the set. rear pads same. I and most people would be totally amazed if the rear rotors needed to be replaced at such low mileage. A sloppy job means an amateur and a sloppy job on a Benz means worse.
Did you get ripped off, be your own judge what the job you got was worth to you. Were you and your car disrespected as well as your mechanics respect for his own work. I think the answer to that is pretty clear.