JustFly review: Airline tickets

Today I twice tried to book a Nov. 2023 Hong Kong Express flight from BKK to HKG at justfly.com. Both times I filled in all the necessary info and, at the very end, their site noted that the transaction couldn't go through. I gave up and booked at the airline site with no problem. I then received an email confirmation from justfly and of course my credit card account was charged. I contacted justfly and jumped through all their hoops, sending them proof of my other booking, etc., asking why would I need two sets of reservations on the same flight for the same people. Then they refused my request to cancel with no penalty because their site had told me my transaction couldn't go through. They said they "couldn't find" a record of this error message. Well, I couldn't produce a screenshot of the actual message at their site -- because I hadn't made one, thinking their error message mean what it said. Wrong. So no "valid proof", no refund. Never mind that it made complete sense. I am going to try disputing the charge with my credit card company, but here's a warning: these people are not reasonable and don't care if it's their fault or not.