Complaint on negligence

I'm a 62 year old pensioner. On the 30.10.2019 I booked my car for service at Kia Motors in Tokai, Cape Town. I took it for service the following day. When I left the dealership with the car after it was done. As I was driving it I realised that it was over heating. I then went to the garage to check what was happening, when the petrol attendant who was assisting me checked, the water and the oil was spitting out, the cap was not closed. I immediately took pictures and called them to let them know what happened. They wanted me to bring the car back and I refused to do as they were the one who supposed to make means to get the car. They then came last week Friday to get the car and I drove with them. They informed me that they will put the car in the machine to check the damage. On the same day in the afternoon when I start it, I realised that it takes longer to start. Saturday evening on the 01.11.2019 when I wanted to leave for church it didn't start, thinking the problem was my battery. I went to go buy new battery yesterday 04.11.2019 but it didn't start with the new battery. The guy who was putting a battery for me said it has the problem with "gasket" the water and oil mixed hence It does not start.

I called the dealerships to let them know of the damage they caused through their negligence and they want me to get the at to the dealership and I have no means to do so. I've already spent R1200 unnecessarily buying a battery which was not the problem. The whole day of yesterday they promised to get back to me and they have did. Please help me. I don't know what else I should do. My car had never given me problems before. I service it all the time. I have the record book of the service. I am so angry. I even regret taking my car to them. If I could undo this experience. I would it without even thinking about it.