When you need help with auto repair billing disputes there are places you can go to register complaints and get assistance. I do recommend that you make your best effort at resolving the issue with the car repair service center first.
A good starting point is to understand what you are entitled to as far as your rights as an automotive service customer. Here is a Government document that does a good job of listing out your rights. The Auto Repair Consumer's Bill Of Rights.
The Federal Trade commission is another government agency that provides a lot of information on the subject of car repair shop practices. You can also fill out complaint forms and open cases on the FTC assistance website. Note: The FTC collects data, they do not resolve complaints.
The FTC has an old article up on their website that provides helpful information for all automotive service customers. Even though the information is dated it still applies to modern day car repair service. A total of nine articles are posted on this next page and all are worth reading! Get some auto repair help from the Federal Trade Commission.
It is always easier to stop problems with car repairs before they start. Communication with your shop is very important and both parties should agree on the actions to be taken before the repairs begin. Don't be shy and ask your service center to explain each section of the repair order to you before you sign it. This document was created for your protection!
If the auto repair business refuses to correct the problem or answer your questions about the bill, legal action is always an option and may be appropriate. Your options for service and repair billing disputes includes contacting the Attorney General's Office in your State, the Better Business Bureau office in your area, and even your local attorney can provide assistance.