very poor service from new vaal motors vereeniging

i took my car for a service at vereeniging mercedes benz on the 11 Feb 2019.My car was driving normal and everything was fine.I dropped it off and later the service advisor called me with a qoutation.which was fine with me.and it was around 10h00 am.around 15h45 she calls me again to ask me if I have had a problem with the car starting.I told her no,because I have never had a problem with starting my car.after 15 min she called me again to tell me that my ECU is messed up and I must buy a new at the price of R26000.How do I pay for something that I didnt break and how do I pay for something that broke at the dealership workshop.I called the service manager by the name of Pauline and she is teling me that the unit has an internal failure.what nonsense is that.I am electrical guy with vast experience.internal failures can be caused by many things ranging from static to overvoltage etc.they worked on my car,it got broken while they were working on it and I must pay.that is total nonsense.I am going to lay a complaint with Mercedes benz SA.they must sort the issue out.this is the second time they do this to my car.they did the same with my sunroof in 2018.they lubricated sunroof,two days later clips are found broken eventually after they opened the roof they ended up replacing the Control unit for the sunroof.in the mean time the car was just in for a simple service.I regret moving over to Mercedes from BMW.i hope someone can help me out with this issue and the New vaal guys.my number is ********** 166