Bad customer service and dishonest workshop

Took my Renault modus in for a major service and to repair a leak. They charged me just over R8000 for this. I drove my car in and was unable to ride my car out of the workshop. They told me my battery was very "low" suddenly and I needed a new battery for R2200. The battery was still fairly new and was puzzled to hear this. I told them I'm not paying so much money for a battery. I called the AA to come and replace my battery and they said there was nothing wrong with my battery. They tested it and they gave me a slip of paper proving nothing wrong with my battery. They then said it looked like a starter motor problem. I was puzzled because I drove my car in for a service and there was nothing wrong with it. I asked Renault to give me in writing the problem with my starter motor. I have heard nothing to date and my car is still in the workshop over a week later. Impossible to phone them as they are always busy and don't receive the messages.