Bad experience

Last year November my car was delaying to start then i took it to tri-sec Volkswagen trichard they charged me R6000 to fix the issue that was on the cylinder 3 later after 6month the car is doing the same problem today I decided to take the car back to the I found the man by the name Hendrik he told me I need to pay for diagnosis for them to check the issue , how can I pay for diagnosis amount of 1900 to for re work on the car because the car came back with a same issue is this fair enough to pay for the same issue twice?