Q.I have a dispute with United Airlines that I hope you can help me with. I recently flew from Venice, Italy, to Miami in business class. I paid for my ticket with mileage rewards.

The day before I was to leave Venice, I learned of a better itinerary, which I was able to switch to, but in Economy Plus.

United billed me a change fee of $100 and an upgrade fee of $129. It definitely was not an upgrade; in fact, it was a downgrade from the business-class tickets I had. I’ve asked United for a refund of both fees, but it refuses. I would appreciate any assistance you can give me to resolve this complaint.

MYRNA LIPPMAN,

Boca Raton, Fla.

A.United Airlines is absolutely correct. The average passenger may look at tickets going to the same destination as you do, which is to say, the business-class ticket is more valuable, and if you accept a downgrade, you’re entitled to a refund. But United categorizes its tickets differently.

Generally, award tickets like the one you booked are classified as tickets that would have gone unsold, and therefore have no value. While the new seat also might have been an award seat, United classified the upgrade from its too-small economy-class seats to its slightly larger Economy Plus seats as a paid upgrade. It also imposed a change fee, which is something it discloses on its website.

That’s something airline insiders understand, but that doesn’t make sense to the average air traveler. And that’s OK. No one ever claimed that this was reasonable. United’s responsibility to you wasn’t to refund the money, but to explain why you had to pay extra. And “because we say so’’ is not good enough.

I list the names, numbers, and e-mails of United’s customer-service managers on my consumer-advocacy website: http://elliott.org/company-contacts/united-airlines/. A brief, polite e-mail to one of them might have yielded a more plausible explanation.

I contacted United on your behalf. A representative called you and explained the fare difference. United also offered you a $150 certificate, which you accepted. Next time, you might want to keep your original flight.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine and the author of “How to Be the World’s Smartest Traveler.’’ He can be reached at chris@elliott.org