Poor workmanship

In December 2014 i took a Ford Fiesta 05 to install an exhaust system with branches at total cost around R4 - 5 k. the system was great an met my expectations. as soon as i drove the car, there was a knocking sound but it got fixed. A few months later i had the same issue and I had to go in out of their workshop on two occasions, a month later they said one of the manufacture brackets was loose and they fixed it. All was good until recently i had a worse issue where the whole exhaust sounds loose as if it will fall apart, I am even worried to take it back to them for repairs as i feel they are very ***********, seems like they don't know what they are doing. How can such a company with experience and good reputation fail to do a proper job. I can,t keep fixing the same thing over and over again.