From Mary Hunt:
If you've ever been billed for merchandise you returned or never received, had your credit card company charge you twice for the same item or failed to credit a payment to your account, you need to know about the dispute settlement procedures provided by the Fair Credit Billing Act (FCBA).
To take advantage of the law's consumer protections, you must write to the creditor at the address given for "billing inquiries," not the address for sending your payments. Include your name, address, account number and a description of the billing error. Send your letter by certified mail, return receipt requested, so you have proof of what the creditor received. Include copies (not originals) of sales slips or other documents that support your position. Keep a copy of your dispute letter. The creditor must acknowledge your complaint in writing within 30 days after receiving it, unless the problem has been resolved. They must also resolve the dispute within two billing cycles, not more than 90 days after receiving your letter.
I have had disputes settled quickly by calling customer service. Make sure you use the words "billing error."
The law says you can withhold payment on the disputed amount during the investigation without fear that you will be reported delinquent or have your credit score affected in any way. To learn more about your rights and the power you have as a credit cardholder, get familiar with the terms of the FCBA at FTC.gov. Type "FCBA" in the search box.
Knowledge is power, especially when dealing with your credit card company.