If there is anything about your bill that doesn't add up, or if charges seem excessive for the services provided, contact the health care provider. If they cannot answer your questions to your satisfaction, you may ask the address for filing a dispute. Let them know of your intention to appeal so that they can make a note of it. Then, start keeping records of every phone call, email and letter. Record the dates, names of those you speak with and what is said.
If you used insurance, call the number on the back of your insurance card to ask the steps for filing an appeal with them as well.
The appeal process may involve several rounds. If you get your insurance through your workplace, your employer's Benefits office may be able to tell you more about the appeals process.
Alternatively, you can consider taking it to small claims court. The "Consent to treat" forms that one signs upon registration do not show the price for services. These are "open price contracts," and according to U.S. contract law, when signing such a contract, a buyer can only be expected to pay a price considered "usual, customary and reasonable"(UCR) for the services provided. By showing the extent to which your bill exceeds the UCR amount, you have another chance at a fair price.
Bills "due upon receipt" often intimidate patients into paying before they've had a chance to check the bill for accuracy. Ask the provider for specifics about when payment is actually due. See also this article from Experian, "Can medical bills hurt your credit?" and the U.S. Federal Trade Commission's Debt collection FAQs.