VW "specialists" who can not fix a VW car

I have a Golf 7 TDi (2014 model) which I purchased from Master Cars in March 2016. At the beginning of November 2017, the car started loosing/using a lot of coolant and subsequently over-heating. I sent the car into Tavcor William Moffet in PE and had to pay just under R1000 for a diagnostics test which revealed nothing and the car was given back to me even though the problem was still there. I obviously gave Tavcor a bad rating since I was not satisfied with their workmanship. I was then called and asked to return the car which I duly did. After my instruction of having someone take the car for a test drive, the water bottle was replaced for R3200 (!!) and the car returned. Not even two days later, I experienced the same over heating problem. I returned the car to Tavcor and after three days, received the car back with the explanation that they had replaced the cap on the water bottle (which apparently does not get replaced when replacing the water bottle). The service adviser said that they will cover the cost of replacing the cap (R700!) but when I checked the cap the next day, it's the same old cap which was on the car. The car is STILL over-heating and loosing/using coolant to such an extent that I have to check the level and top up every single time before I can drive somewhere. I really fail to understand how a company who specializes in VW cars, can not find and fix the problem. In addition, after all the inconvenience that Tavcor put me through, I was never offered a courtesy car and therefore spent a lot of money on Uber trips. I'm really disappointed and will never recommend Tavcor William Moffet, PE to anyone.