Dear Liz: I have a dispute with a credit card company over an online transaction that I canceled. The company charged me three times but refunded only one of those charges. The credit card company initially canceled the other two transactions but I was rebilled without my knowledge. Despite my submitting evidence and the card company agreeing that I don’t owe the money, it will not take the charge off. Who do I contact to get this settled? When I call the card company, they say they will look into this and contact me in 10 days, which they never do.

Answer: It’s convenient to dispute credit card billing errors over the phone. If you want to preserve your rights under the federal Fair Credit Billing Act, though, you need to put your complaint in writing.

Your letter should be sent to the address given for billing inquiries, rather than the address where you send your payment, according to the Federal Trade Commission. The letter needs to include your name, address and account number along with a description of the problem. You should send copies of any receipts or other documents that back up your case. The letter should be mailed in time to reach the creditor no later than 60 days after the statement with the error was generated. The letter should be sent by certified mail, return receipt requested.

That’s a cumbersome process, and often not necessary for people who monitor their statements and catch a problem early. Ideally, they first would contact the merchant and give it a chance to correct the problem. If the merchant doesn’t do so within a few days, the customer can contact the credit card company and give it time — say, 30 days — to resolve the situation. If that doesn’t work, then the customer can fire off a letter.

Even if you’re now outside the 60-day window, you should still send a letter and ask for a prompt response. If you don’t get one, you can file a complaint with the Consumer Financial Protection Bureau, which intervenes with credit card companies to resolve such disputes.