Disgruntled Customer

I am so so disappointed. I own a 2019 VW polo DSG. A smooth car, as a lady I ensure my car is serviced on time always. I recently tried VW Constantia Kloof in Roodepoort as it’s closer to work. I was happy that they did all which was required. A week later my car mulfunctions. They charge me a diagnosis for something they should have picked up a week prior which was my spark plugs. I am furious. It’s middle of the month, i use my car to travel to work and thus meaning i am at their mercy to repair at their inflated prices. Im upset and will not be using them again