DOT issued a Warning Letter to call carriers earlier today reiterating long-standing rules classifying lengthy delays as qualifying for a refund. It offers not to bring enforcement actions -- in light of the emergency -- for those carriers which, having offered a voucher, now process a refund. Whether "substantial" is 2 or 3 hours is an open question. But, one would think that 10 would qualify.
Consider filing a DOT complaint along with your chargeback.
https://www.transportation.gov/sites...3%202020_0.pdf