Bad service and poor customer service

We bought a c180 from wonderboom Mercedes-Benz in 2017, from 2018 we started having problem with the engine light popping on the dashboard, the car was still under service plan, so we would book it in under the impression that they are fixing the problem and only for the problem to resurface again after some few months, this happened until the car was out of service planand. when we take it back for the last time, they gave my husband a courtesy car for almost 2 months and they still say they couldn't find a problem BUT have done a valet wash on the car, some of the things where broken when they returned it . When we complained about them they said the car came in like that. To cut the long story short, we parked the car because we couldn't drive it and couldn't afford to have it fixed by the time. Beginning of May 2021 we took the car to Interfix in Pretoria North for it to be fixed. And the part that was taken out as the cause of the car to have engine problems is evident that the problem started the day the engine light started to flick. They did fix the problem but we feel like we cannot be payimg for things that was obviously from poor workmanship, bad customer services and ignorance. We will be calling ombudsman so that they can help us going forward.