Bad service and not being honest to customers

I took my car for a service at car service city in Centurion CBD. When I left the car was losing power when I drove. When I called the service manager didn't even let me finish speaking told me to bring back the car they will reset the service light and all my problems will dissappear. I went back and that's when he told me the ignition coil rack was damaged I need to replace it. When I asked why didn't I have this problem before I brought the car to them he said that it is an electronic part they couldn't have known when I asked if they picked it up on their testing machines they said tge machine didn't pick up the problem, which doesn't make sense to me. How can they not pick up the engine light going off. Makes me even more angry is I can hear them talking about me as if I'm a crazy person because I'm asking questions. Customers are their bread n butter but have no respect for them. They damaged my baby because it doesn't make sense to me that a car has more problems leaving a service centre than when it went ot.