Failure to do proper service on the car

I took my Mercedes to them for B1 service on Thursday 6th August 2020, the car was in good condition when it went to them, it came back with an engine light on and it didn't want to pull, on acceleration, the car was taken back to them this morning they say it's a cable failure it has nothing to do with the service we have to pay an additional R2900 for them to replace the cable. The same thing happened in 2017 or 2018 the car went for service in good condition and came back with an engine light on not wanting to pull when driven and we were told it's a different thing which has nothing to do with the service and we were made to pay an additional amount. How come they do not pick up the problems during the service and not give us the car to go and get stuck on the road. I trusted Mercedes Benz dealers so much but now I am so worried that each time you take your car for service you create problems which never existed on your vehicle. I suspect there's something going on with the people that service the vehicle, can this be sorted out once and for all. I am really frustrated and tired about this whole drama. To add a filter was sent with a driver to come and fit it in as they said it was not in stock.