Car Service City Fairviev Gqeberha

I took my Polo TDI 1.6 for a small diesel leak at the injector leak off return pipe, was quoted it was just a small 8mm o-ring replacement. Paid for fix and two hour labour, but it still leaked a little. Took it back the next day, was told it's the inject o-ring, but can't get hold of it and use tape and silicone to fix it. NOW my car that was driving perfect it making a loud noise(diesel knock i was told) and misfiring. I was it might sort itself out? How can you guarantee workmanship like this? A perfect car is now worse off and I had to pay for it! This is really poor service from Fairviev Gqeberha branch Today their complaints department basically told me that they are not responsible, they fixed the leak even if they broke an injector to do it, they really don't make sense or want to take accountability for their actions. POOR SERVICE!