Wrong diagnosis on the car

So Monday morning the 12th August 2019 while we just checked out of our hotel. Our A5 Audi gave a sign of on the screen. The sign was coolat or so. We took the car to the nearest Audi Centre which is Audi Centre Cape Town. Upon our arrival they assisted us quite quick since we did mention that we were on vacation and we are heading to Johannesburg. They brought us the tax invoice of what need to be done and the amount to be paid. We were comfortable with it and gave a go ahead for them to fix the problem they diagnosed. Little did we know it was the beginning of our problems. We asked to be taken to V&A Waterfront to buy time while they are busy and they must call us when they are done. When they were not so done they called us that they did replace the part accordingly but the car is still overheating. My husband went there to understand. When he arrived he told me that things have changed more things need to be replaced and the amount is too high. I went there to get more information. Browny Forbes the lady who was assisting is tried to justify their actions but we feel we were ****** by Audi because they replaced a part which didn’t need to be replaced at all and we were charged for that only to be told after the car was not fixed that we need to part for other things because the car is not fine. I’m of the believe that they did a guess work and in the process they have costed us money. When we took the car to be fixed the people who fixed it made it clear that there was no need to replace the coolat tank because it had no problems at all. The problem was something else. They took advantage of our desperation since they knew were had to travel very far. I need someone to get to the bottom of this issue and be resolved. We need our funds back that they charged us for their wrong diagnosis and replaced a part that didn’t need to be replaced.