Kohler Motors Witbank/Emalahleni- Negligence

I bought my Chevrolet Cruze hatch back 1.6 vehicle in 2013 brand new and all the car service maintenance has been done by same company and up to date. From January 2019, I started experiencing some issues with my vehicle it was showing engine warning sign and the slippery warning sign. I then decided to take my car to them to check what the issue was and I was referred to the manager then a Mr Wayne. I explained to him what the problem was. He then took the car for inspection and I waited for him to finish. He then came back to me and said that the car was fine and there was nothing wrong with it. He also said that he drove the car and its in good condition. He then gave me back the car and I left. On the 19th February 2019 same situation happened again with the engine and slippery warning sign and I took the car back again to Kohler Auto. The took the car and they inspected it and they said they suspected the crank sensor to be a problem. They gave me back the car and said if it happens, again I must come back. On the 14th March 2019 again same issue happened and I went back again to Kohler Auto and this time around they changed the cranked shaft sensor and replaced with a new one and they said that was the problem. They gave me back the car and I used it with the thought that all the issues were gone and the car was not finally fixed. On the 6th July 2019 same thing happened again the engine and slippery warning sign came up, as I was driving from Witbank/EMALAHLENI to Ogies the car just stopped and locked itself. I then called my insurance and they came and towed the vehicle to Kohler Auto in Witbank/EMALAHLENI. Monday 8th July got a call from Kohler Auto and a woman by the name of Thalitha wanted to confirm with me if they can start working on the car to check what the problem was. I gave them the authority to check the car. From their feedback they said that when they opened the car they found that the water tank had burned, the tank was empty, and that damaged the engine. Thalitha from Kohler Auto also called me and gave me a quote to replace that engine with an amount of R85 667.45. This is when I truly felt that Kohler Auto was unfair and very ***********. As mention before I had taken the car to them overt 3 times this year with the same issue and they kept telling me that the car was fine. A sensor was changed but how did they not see that the tank had a problem. Why was this not picked up before and now I’m expected to pay so much money over their incompetence and negligence. I then made an appointment with them and I went to the workshop and spoke to a Hennie as the previous manager Wayne had resigned. I explained everything to him and how the car had been giving me trouble and how many times I had brought it in and none of his team members ever picked up that the issue was the water tank. He then told me that I am responsible for the car and should have checked the water levels. This made me very angry because if they were competent enough and had checked properly they would have recognised or found the issue a long time ago.