Mc Carthy Kunene Witbank-Damaged my sump plug, which nearly causes engine to cease

Hi, on the Friday, 01 June 2018, I send my vehicle for a service at Mc Carthy Kunene Witbank in Witbank. The following Monday I drove to Limpopo for work, and when in Limpopo I realized that there is an oil leak under the engine. I then informed Mc Carthy Kunene Witbank about this and they said its only the oil that was left under the engine bracket cover during service. As I was driving in Limpopo I realized that the leakage is getting too much. I then went to the garage to check and the oil stick shows that the oil was way too low, which can cease the engine. The oil was coming out of the sump plug. I was then forced to top it up. I then called Mc Carthy Kunene Witbank again, and they said I should bring the vehicle when I'm around Witbank again. I told them that my work allows me to travel month-end because is 410km to be in Witbank. Month-end I got an opportunity to meet them. They then used a *****(not original body part) for the sump plug, they told that the threads on the sump plug are worn out because my vehicle is old. They then gave me a R+-R16 000 Quotation for a new sump. I then told them that I was not the one who broke the sump plug, but them, but all was in vain On 27 November 2018 I then took my vehicle to a similar supplier, and I was charged R17 000 for replacing a sump. I THEREFORE WANT TO CLAIM MY MONEY FROM Mc Carthy Kunene Witbank because I was not the one who broke the sump plug, but them. Your assistant is highly appreciated Regards