Q. My husband and I recently flew from Mexico City to Fiji for our honeymoon. One leg of our flight between Los Angeles and Fiji was canceled by United Airlines. We booked tickets on a different airline for that portion of our trip.

Due to bad weather, our return flight from Fiji to Los Angeles was delayed 24 hours and we missed our connection to Mexico City on United Airlines. As soon as I knew we would be missing our flight I called a United representative, who rebooked us for a flight the next day. I paid a $150 change fee per ticket. I understand this charge and am fine with this transaction.

Here’s my problem: Somehow, my mother’s card was automatically charged $869 for two tickets from Los Angeles to Mexico City. I asked about how the charge got on my mother’s card in the first place, since I had used a different card for the original purchase and that I was required to pay the $150 change fee at the airport.

The response was that my mother’s card must have been presented at the ticket counter or provided over the phone. The only place it could have come from was United’s system. Can you help me sort this out?

Robin Griffith

Mexico City

What a mess. United shouldn’t have charged your mother another $869, but after reviewing your itinerary, it shouldn’t have billed you for a $150 change fee, either.

When United canceled the Los Angeles-Fiji leg, it refunded the value of that ticket. You rebooked another ticket on your own. Had you linked your tickets through the same reservation number (a travel agent can do that) then United wouldn’t have charged a $150 change fee.

I’m not sure why United charged your mother’s credit card, or how that was even possible. I know that while you were honeymooning in Fiji, United was having some problems with its reservations system, which may explain the mystery ticket.

The key to resolving a problem like this is documentation. Keep all your receipts and boarding passes so that if there’s an erroneous charge later, you can prove you were billed incorrectly. This is particularly important when you’re dealing with a cancellation or some deviation from your intended schedule. That’s when things can go wrong.

I contacted United on your behalf. It refunded the $869 charge to your mother’s credit card.