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：如果航空公司给你一个航班积分，而不是为他们取消的航班退款，你可以向美国运输部投诉，试图获得退款。