I R2550.00 for services not rendered

Supa Quick Pinetown 109 Old main road. Last year 4 October 2018, i took my car in to change the rear silencer drum. Hyundai ix35. I paid R2550 for them to get me this new drum. to my suprise when I brought the car in to be fitted, the drum was way smaller than the original drum. Which resulted to the driver to make very strange noise almost like its a car with 2pipes or those sports cars. When I asked why the drum is smaller they said it wont any difference and that is how they make it. I tell you the car is noisy and if you know the Hyundai cars you will understand what I am talking about. It also makes a lot of noise as the drum is smaller so it moves side to side when driving and rattles to a point that i feel like i am driving a truck. I went to complain to Supa quick in November since they told me to give it a month after fitment. Lucky, a guy who helped me was not very friendly and helpful about my complain. We ended up shouting at each other. In the end he said he will find the new drum in the correct size and they will remove and fit the new one for free since I have already paid. He wrote down in his book, and told me to wait for his call once the drum arrive. Up until this day, the 17th of May 2019, I am still waiting for Lucky to call me. I am still driving the car and the noise gets worse everyday. I would really like to know from the management of Supa Quick Pinetown how long does it take to get what they promised a customer? Lucky had all my details, and in their system as well.