To keen to take your money and not quite to resolve

I was there thinking they would find the problem with my car they said that my air and petrol mixer was incorrect so I believe them, they said that the problem within the air and petrol is causing my spark plugs to go black the results is that the plugs stop working so my car gets fluid, the guy that helped me said he is 99% sure that is the problem after I asked him is there anymore issues he said no, a week latter the car is doing the same thing I call back asking for the mechanic to please call me back I followed up 3 times and they kept tell me the same thing we will get someone to call you back and no one calls if I have to say I am very disappointed as I Spent R1000 on this job and was willing to pay what ever it cost to fix my car, yeah to quite to take the money and not to keep to resolve the problem, guys I wouldn't recommend this branch.