Immediately write a letter to the customer service department of the card issuer. Give your name, account number, an explanation of the error and the amount involved. Enclose copies of supporting documents, such as receipts showing the correct amount of the charge. You must act quickly -- the issuer must receive your letter within 60 days after it mailed the bill to you.
Under the federal Fair Credit Billing Act, the issuer must acknowledge receipt of your letter within 30 days, unless it corrects the bill within that time. Furthermore, the issuer must, within two billing cycles (but in no event more than 90 days), correct the error or explain why it believes the amount to be correct. If the issuer does not comply with these time limits, you don't have to pay $50 of the disputed balance.
During the two-billing-cycle/90-day period, the issuer cannot report the amount to credit bureaus or other creditors as delinquent. The issuer can charge you interest on the amount you dispute during this period, but if it later agrees that you were correct, it must drop the interest accrued.
