Overcharging and rude when they are confronted.

I took my chev aveo for a major service to Fix It in Heugh Road Walmer. What a disappointment. Not the service but the owner and the lady in the office. They advertise a major service for R750 that includes replacing the oil, all top up fluids, 4 new spark plucks and new oil filter. I requested them to put in high mileage oil, to replace the timing belt and all filters. The lady told me that the service fee will be R1200 that I agreed on. I asked them to do the wheel alignment and pollen filter next door at the aircon business. She phoned a hour later and told me that the cost will be R1800. I agreed on that. When I arrived to fetch my car the lady produced an unspecified invoice for R4150. She then produced another invoice showing 6 hours labour for fitting the timing belt.. The person who replaced the timing belt informed me that it took him 2 hours. The lady then informed me that the owner instructed her to charge 6 hours for labour. After confronting him he gave me back R300. (They already had R4000 in cash from me). At that point the lady told me to leave and never come back, she told me that the owner agrees with her and that they will not be refunding me