Midas Elardus park refusing to pay for ECU they broke

On the 8th September 2020 I drove my Nissan Navara registration to Midas Elardus park workshop, as it was in limp mode. The computer was used to diagnose the fault and I was informed that it was due to a fault on injector No 4. The mechanic named Hendrik then told me that it was a quick repair as he just needed to change the tip of the injector to remedy the problem. Hendrik then ordered the part and installed same. This did not remedy the problem. Hendrik the mechanic then continued the diagnostics and informed me that his conclusion was that it was the Engine Control Unit ( ECU ). I then questioned what the way forward concerning the repair to which he informed me that there was a company in Pretoria West that could repair the ECU. I then instructed him to take it to them to which he informed me that it would take a day and that he would get it back from them on Thursday the 10th. When I contacted him on the Thursday he informed me that he had not taken the ECU for repairs. I then informed Deon who are the owners of Midas Elardus Park about his conclusion to which they responded that I should get a second opinion. When I informed Hendrik the mechanic what I was told to do By Deon, he started getting very upset and informed me that he had more than 30 years experience in the automotive trade and that he would repair the problem. I told him to put the parts back into the vehicle as I wanted to drive it away for a second opinion to which he responded that he was very busy and would do so when he had the time, I then informed him that I use the vehicle for my business and need it urgently to which he responded that I must not to worry as I am in good hands and should leave it to him to repair. I did so and when I arrived at the workshop on Friday the 11th to inquire about the repair I saw that the ECU was lying on the side of the engine and that the cover that protects the electronics had been forced open to which he informed me that he had tried to repair the unit but had not reinstalled it. I left expecting it to be running by Monday the 14th. On Tuesday I went back to Midas and informed Hendrik that he should put the vehicle back to the way it was when I brought it there, as I wanted to drive it to the auto electrician to repair it. After he had put everything back together it would not start. I then informed Deon the Owner of Midas Elardus park of the problem, and he then informed me that it was not his problem as the mechanic was not employed by him but only rents the workshop from him. Had I known this I would not have taken the vehicle there but rather had taken it to a reputable workshop. Deon then said he would contact another auto electrician to attempt to repair the electrical fault. I then left to attend to a job. I returned to the workshop at about 2:30pm to find out what the conclusion was from the auto electrician and Deon informed me that the auto electrician found out that Hendrik had done soldering on the ECU and now it was now damaged beyond repair. Deon then told me that I must buy a new one if I wanted the vehicle repaired and also said that he had now lost R2500 rand as Hendrik had worked on my vehicle for 5 hours. Deon then said he could fire Hendrik. If Hendrik is not in his employ then how could he fire him? Deon then informed me that I should investigate where I can buy a new or second hand ECU at my expense to replace the ECU that his mechanic had damaged beyond repair The vehicle at this time has been standing unrepaired at the Midas Elardus Park for 7 days and as it is not running. I had to tow my vehicle to auto electrician who replaced the ECU at a cost of R11800.00 Which Midas Elardus park are refusing to pay even though they damaged it. In other words they the owner is not taking responsibility for his mechanics mistakes