I think I've recieved poor service and been overcharged. What can I do?

Is there an organisation or government department in The Netherlands I can go to for help or to register a complaint? I think the mechanic who mended my car is trying to get a lot more money out of me than he should for a job that took less time than he said. I don't want to pay this bill, even though I've asked him about it. Seems like he's trying to "rip me off"! In Britain there is something called Trading Standards that can intervene to see if traders are conning people. Is there an equivilent organisation here? Many thanks in advance!