Very poor service

I am very disappointed in the service that l got from Volkswagen table view. I took my car to them as l was having a problem with ABS, steering wheel and hand brake lights flashing on my dashboard. I was assisted by Monique Dalhouzie the service agent. They did a diagnosis on my car and told me l needed to buy a new battery and earth cables to get the problem resolved. I did exactly that and gave them to go ahead and replace the things they had mentioned as l trusted that they knew what they were doing as they had done a diagnosis on my car. After they were done with the vehicle, l took it home, the following morning l realised that problem is still not resolved. I took the car back to them and they checked it again and said there was a broken cable and they fixed this cable. I took the car back home and the problem was still not resolved. I took it back to them the 3rd time and now they tell me the alternator has a problem. I did not trust them so l told them l am coming to get my vehicle and went to test the alternator at a company that deals with testing and repairing of alternators and they confirmed that there was nothing wrong with the alternator. I complained to the manager Trevor Hodges and requested that l wanted them to refund my money and the manager refused to refund me as he said that what they replaced on my car still needed to be replaced even though they failed to resolve the problem. Now they wanted me to replace an alternator that is working.what could have happened if l had replaced this alternator and the problem still occurred l could have lost so much money.