CIB insurance cruelty

I was involved in an accident on the 09/08/2019. The car that I was involved with was written off and the driver of the car even ran away knowing that he was at fault. My car was badly damaged. The assessor went to check my car where it was towed to, in my presence. According to the assessment, the car was already close to the write of value by only checking the cosmetics and had they assessed the engine part was definitely going to be a write-off, however that could be done as the engine was not running, but they assumed that the engine was fine. I raised this matter with the insurance and I was told that if the car gives mechanical problem they'll fix it. During the repairs indeed the car reached a write off value. The assessor called me and advised me and I agreed with him that they should write off the car ( money spent was approximately R200k and the value of the car was R450k). He came back to me and said his manager was against it as the repairer advised him that the only need to buy a part that costs R7000 and the car is ready. I then reminded them again that they don't know the engine conditions and they still needed to check it. I got my car on the 5th of Dec 2019. The repairer guaranteed me that they check all the electronics and everything is fine. Test drove the car for approximately 20km and didn't experience any problem. I took the car and drove for 50 km and when I pressed it on the steep it started losing power. I advised the insurance and I was told to take the car back to the repairer and the repairer noticed that there was oil all over the engine. They lifted the car to Mercedes Benz Menlyn and it was confirmed that the turbo and the catalytic converter were damaged. The assessor appointed their own agent to look at the issue if it was accident-related. The agent found that the repairer did not change the catalytic converter even though it was quoted. And blamed the repairer. The agent suspected that the damaged catalytic converter caused back pressure which blew up the seals on the turbo. The cost of replacing both the turbo and the catalytic converter was R114k and there might be more damages in the engine. The insurance rejected the report that was coming from their agent and said they needed to get their own mechanical expert. According to the report from their mechanical experts the damage to the turbo was not accident related and as for the catalytic converter there are 50/50 chances that it was not accident related, even though there are fents on the catalytic converter. And as for the replacement of the catalytic converter which was not replaced by the repairer is now my responsibility to take up the issue with the repairer. This is the treatment that I suffered from this insurance and I don't even have a car as we speak.