You've called your card issuer about an unauthorized charge or merchant billing mistake. Or you're still stuck with a billing error that the merchant failed to quickly correct.

Now it's time to write your card issuer.

Summarize the earlier phone call or attempt at resolution with names and dates, and state what you want the company to do. If you have any proof the charge wasn't really yours, include that.

However, you're not required to have proof to dispute a charge, says Ruth Susswein, deputy director of national priorities with Consumer Action.

When you're ready to send your letter, mail it certified with a return receipt requested. That will give you proof of the dates your letter was sent and received. Keep copies of any letters you send, along with any notes of the phone calls you made earlier.

Mail the letter to the address for billing disputes, not the billing address, says Susswein.

The issuer must acknowledge your credit card dispute and send written acknowledgement within 30 days of receiving your notice. Promptly complete any forms the issuer sends you and mail them back certified with a return receipt.