If an airline refuses to refund a cancelled flight that you are legally entitled to (such as under US DOT rules or EU 261/2004), your first step is to file a formal, written complaint with the airline's customer relations department, explicitly citing the relevant passenger rights law. If they still refuse, you should initiate a "Chargeback" through your credit card provider; provide the bank with proof that the flight was cancelled and that you attempted to resolve it with the merchant. In 2026, most major banks have streamlined this process for travel disputes. Additionally, you should file a complaint with the Department of Transportation (DOT) in the US or the relevant National Enforcement Body (NEB) in Europe. These agencies track consumer complaints and can fine airlines for non-compliance. Finally, if the amount is significant, you can look into "claims management" companies that take a percentage of the refund in exchange for handling the legal work, or take the airline to small claims court, which is often a surprisingly effective way to get an airline's legal team to settle the refund immediately.