Golf 4 TDI 2005 7months at VW and still not fixed

October 2014 the engine warning light started flashing and the vehicle lost power intermittently when driving it. My father took the vehicle to McCarthy VW in October 2014. They diagnosed the problem to the wiring harness and replaced it. This proved not to be the solution and the car still had the same problem. The vehicle was then referred to a different technician which diagnosed the problem to be a faulty cylinder head. Still the problem persisted. The technician then diagnosed the fault to be the injectors. The injectors was refurbished and calibrated by Northern Diesel at a cost of R13,000 paid to Northern Diesel. VW refitted the injectors. Still the problem persisted and the technician said the injectors was the problem, they were taken out again, taken back to Northern Diesel who tested it again. The car was ready to be collected in April 2015 after 7 months at VW. My father drove the car back from the dealership and the next day the car had the same problem. My father took the car back on Tuesday the 19th of May 2015 only to hear two days later that another car reversed into his car at VW's premises. VW is refusing to fix the damages to the vehicle in the expected manner.