Not happy with VW Hatfield

I went to service my car at VW Hatfield Bryanston, Since January I'm not happy because till today the car is not right. The cat went for a major service then they told me it will be ready the following day. I booked it on a Monday and I got it back on a Thursday afternoon. Then I called again to tell them that I'm not happy with the car. They told me to bring it the following week. then I was told the aircon pump Is not working. I asked then how so because it is in a same place with the V-Belt and it was working. I was told its not they problem but we fixed it now again day after I collected it a car gave me an error that 12v its not charging. again it is something that has to do with the V-belt. Now again I'm told its my fault however everything was working perfectly before they charge this V-belt. I think the technician is not doing his job right but the blame is on me even though we did not drive a car that much. they first quote me R2500 and now is R6000. All these thing happen after they change V-belt. The aircon pump and the alternator are control by this V-belt that they charge. why do I have to pay for what they broke