A: Overbooking, or selling more tickets than seats, should be illegal. But in the upside-down world of the airline industry, it’s a common and accepted practice. The only thing stopping an airline from overselling more seats are Department of Transportation regulations that require an airline to fork over a refund, and then some, if it can’t get you to your destination.

Your rights are outlined in the DOT’s brochure FlyRights, which you can find online: www.transportation.gov/airconsumer/fly-rights.

American Airlines should have offered you a written statement describing your rights and explaining how it decides who gets on an oversold flight and who doesn’t.

You were entitled to denied-boarding compensation in the form of a check or cash. Based on your correspondence, it appears that you received none of those things, which is a clear violation of DOT regulations.

You could have sent one last appeal to American Airlines (I list the executive contacts on my site: elliott.org/company-contacts/american-airlines). You also could have filed a complaint with the DOT online: www.transportation.gov/airconsumer/file-consumer-complaint.

I contacted American and your online travel agency, Travelocity, and got to the bottom of the mystery. Travelocity’s records suggest that you missed your flight, not that you were involuntarily denied boarding. But your online agency contacted the airline to see what its records say, and after some back-and-forth, American agreed with your conclusion that you’d been denied boarding. American paid you three times the value of your ticket, in accordance with DOT regulations.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine and the author of “How to Be the World’s Smartest Traveler.” You can read more travel tips on his blog, www.elliott.org, or email him at chris@elliott.org.