What are some legal actions I can take if a mechanic rips me off?

Is there something I can threaten to report them to if they don't treat me fairly? The engine was having trouble starting, did some weird stuff while idling, and it had a check engine light. Now all that is fine and runs OK but the Airbag light is on, the steering wheel isn't straight and the blinkers don't work, and they want to charge me for fixing those problems when I didn't have them before they fixed the other problems.