Disgusting serivde and product

My car broke switched off on umhlanga rocks drive yesterday morning, I contacted Mercedes road assist after a very long wait I had road side assist get to me, to cut a long story short the towed the vehicle to their workshop, they said they wee going to let me know asap what the problem was, they did not call me I had to call only to be told that they had not attended to the vehicle yet, when they did call me they told me there was a problem with the fuel pump and had to order the part from JHB , I was then a bit relived that they had found what the problem was, I got a call this morning from the service adviser asking me when last I filled rule , where I filled up as they thought it was the fuel pump but it was not, makes me wonder ()they pride themselves with service excellence) what kind of diagnostic tools do they use ??? what kind of technicians do they have, I called to speak to the workshop manager who was (as usual in a meeting) they still don't know what is wrong with the vehicle, (makes me wonder) the quality of workmanship that goes into a branded vehicle like Mercedes( do they take their products for granted??? Mercedes Benz think again ,