Unhappy customer

The insurance approved an auto repair centre whom I think is not certified by Toyota (auto magic witbank. They used second hand parts to fix my vehicle and after a week I went back to them to complain and they said they will contact the supplier of the parts and they will replace them, it has been four weeks now and I still have not heard anything from them, I called my insurance on 28 November they also said someone will contact me in 48 working hours, it's been a week now and still I have not heard anything from them. I'm really unhappy about the level of service I have received from both these companies.