YSK: If an airline gives you a flight credit, and not a refund for a flight that they cancelled, you can file a complaint with the US Department of Transportation to try and get your refund.
from /r/YouShouldKnow
YSK：如果航空公司給你一個航班積分，而不是爲他們取消的航班退款，你可以向美國運輸部投訴，試圖獲得退款。