Returned Car With Engine Warning Light

Booked my car in to get my one of the rear lights, brakes and wipers fixed on the 21st of April. When I went to collect the car a couple of days later, a warning light was on on the dashboard. Manager said it was because of the keycard battery, I told them that wouldn't be possible. He then said it's because the car needs to be serviced, and I said that wouldn't be possible because one was recently done. They then concluded that they will keep the car and get the light sorted. I was then told it was because I had the wrong battery on the car and I asked why wasn't the warning light on when I dropped the car off if that's the case. I escalated the matter to the head office and a complaints consultant called Lerato Maake told me she would investigate, only for her to then tell me her colleagues told her the warning light had already been on and that I'd have to fetch the car and go get it checked somewhere else myself because they'll start charging me storage fees. I refused and she told me she will get back to me with feedback after I sent her proof that the warning light was not on when I brought the car. I have had to use public transport for over a month and nobody has even bothered to give me any feedback or updates unless I call or email first. I expressed numerous times the inconvenience this matter has caused and that I had been in the process of selling the car and that deal had fallen through and lost me R100k but nobody is bothered. Nobody has offered me an explanation why a mechanic company would fail to fix a car issue they caused for over 70 days.