Since global travel shut down in March 2020, thwarted passengers have been asking a version of the same question: Where’s the money for the trip I couldn’t take?

The Department of Transportation said in a report last month that in the 18 months starting in January 2020, it received 124,918 consumer complaints related to air travel — more than 84 percent of which were about refunds. Before the coronavirus pandemic, the department received an average of 17,420 aviation complaints a year, with just over 8 percent related to refunds.

Airlines “have been absolutely awful,” said William McGee, aviation adviser for Consumer Reports Advocacy. “We have put more energy into this single issue than any other airline issue that we have advocated for over the last 18 months or so.”

He said the organization started collecting stories from people who were having refund problems in March 2020 and were “inundated.” Complaints from people struggling to get their money back continue today.

“We’re talking about people that have booked as recently as a month ago,” McGee said.

Airline meltdowns such as Southwest’s over the weekend — resulting in more than 2,000 cancellations — typically put a new focus on the subject. Carriers are legally obligated to provide refunds if they cancel or significantly change a flight.

In the months after the onset of the pandemic, the Department of Transportation said, airlines had a hard time processing the volume of refund requests that they received.

“Many airlines were also initially reluctant to provide the required refunds,” the department’s report said.

Since then, the department said, it had launched investigations into 20 airlines for their failure to provide timely refunds, 18 of which were still pending last month. It also issued a complaint against Air Canada, seeking a fine for its delayed refunds, and increased the number of staff members assigned to handling consumer complaints.

Nine airlines, according to the department, amended their policies to make it clear to passengers when they are entitled to a refund, and they are providing those refunds as required.

“Thousands of passengers who had initially been denied refunds have received or are receiving the required refunds,” the report said.

The department is also starting the process of exploring rules that would enhance consumers’ rights if a flight is operating but a passenger decides not to fly because there are government restrictions.

Advocates say another category of traveler is left out: people who were sick with covid-19 and couldn’t travel, those whose events were canceled, and travelers who were under a doctor’s order or public health guidelines not to fly.

“In that category, airlines have generally refused to provide a cash refund,” said Paul Hudson, president of the passenger advocacy group FlyersRights.

Earlier this year, a ruling by the U.K.’s Competition and Markets Authority had bad news for travelers. The authority said the law there does not give passengers the right to a refund if they are legally prohibited from taking a flight because of government-ordered lockdowns.

Airlines have offered passengers more flexibility than they did before the pandemic, offering vouchers or travel credits when refunds were not available. But many came with expiration dates or went to people who had no idea when they would feel comfortable flying again.

Experts say those who believe they are owed a refund but haven’t had any luck should take these steps:

Take it to the DOT

Travelers can file a complaint with the Department of Transportation on its website. The department suggests first giving the airline a chance to resolve the issue at the airport or after you file a complaint with the carrier.

Keep trying with the airline

McGee said his “all-bold, all-caps advice” is to be persistent. He said the success stories he hears usually come from people who try — by calling or other means — five, six or seven times.

“You can’t make one call and expect to have it done,” he said.

Complain on social media

Sometimes efforts that haven’t worked on other platforms can get a response if a passenger complains on Twitter or Facebook, experts said.

Turn to the credit card company

If the airline did not provide a service, consumers can dispute the charge on their credit card — though this option is time-sensitive. McGee said travelers should always book with a credit card so this remains an option.

Ask an advocate

FlyersRights offers tips on resolving refund issues. It has a hotline set up at 877-FLYERS-6.

While consumer advocates said they are glad to see the DOT’s report — and have met with officials to press for passengers’ rights — they want to see the department do more.

“There’s a lot of people who simply do not want to fly,” McGee said. “The amount of the refunds can vary tremendously ... and people need that money. They don’t need airlines to earn interest on that money.”