Poor job

Last year my insurance company assigned me to submit my car to renew-it Sandton for repairs, when collecting the car I did not notice the paint drops and the polish that was used when I realize that I took it back to them, they said it will take days to fix that and I said but I will need a courtesy car and they promise me that when their courtesy car is available they will let me know and that was January and now they tell me about the amount that I must pay for the car which I'm not prepared to pay because they've done a poor job. If they've done a perfect job as they always say in their adverts we won't be having this problem maybe their Head Office can help me with this situation.