https://www.siliconvalley.com/2021/12/13/travel-troubleshooter-frontier-airlines-promised-refund-went-awol/

DEAR TRAVEL TROUBLESHOOTER: Frontier Airlines canceled my flights from Minneapolis to Denver last summer. I requested a refund since the next available flights were significantly later. Consequently, these Frontier flight cancellations qualify passengers for a refund under Department of Transportation regulations.

I have spent hours on hold with Frontier and talking to agents. When Frontier canceled my flights, a phone agent said they were able to find all of the payments I made by credit card and that every single one would be refunded to my Visa.