Poor service

I had a problem with my vehicle and took it to the Pinetown dealership. I was immediately advised that Motorite (the company with whom I have my motorplan) would not pay for the diagnostic and I would be liable. After the diagnostic was done a part was swapped around etc and then the coil pack was replaced. Before replacing the coil pack I was told that there was a further amount not covered by Motorite which I would need to pay. It had already been two days and I needed my car back so I paid an took delivery. I then queried with Motorite why the full claim was not paid. I was advised that Mercedes Pinetown carried out unnecessary work on my car in order to bill me and make more money however some of the work was not needed since the diagnostic pin points the problem and there is therefore no further trouble shooting required. I explained to Motorite that I was unaware of this and therefore paid to pick up my car. Since I was out pocket Motorite then approved the claim in full and Mercedes Pinetown refunded me. Despite this the fact remains that Motorite is alleging that Mercedes is overcharging customers so I wrote to head office to query this. I also asked for feedback in writing and not telephonically as I wanted to take this back to Motorite. I received an email from Monageng two weeks later advising that I was refunded and the complaint would be closed. Monageng clearly did not investigate the reason for my complaint and just felt that since the refund was paid that the problem was solved however if Mercedes is conducting unnecessary work in an attempt to over bill customers then this is an ethical concern and warrants investigation. I am just trying to figure out where the problem lies, whether it's Mercedes or Motorite so that I do not have a repeat of this in the future. However since Mercedes has not bothered to look into this and just closed the case it makes me question 1, is Motorite correct and are they just sweeping this under the carpet or are the customer care agents too lazy to investigate. I look forward to hearing back from Mercedes on this matter but until then beware if you use the Pinetown dealership.