The DOT complaint system is speedy and effective in this situation. While DOT does not enforce individual matters, it does forward complaints to the carrier with the requirement that they respond to the complainant and provide a copy to DOT. As US rules require a refund where there is a cancellation, there is no option for the carrier other than to issue the refund and then report that a refund has been issued.

I would also not hesitate to initiate a chargeback, No reason to wait,