Reservations – Flight registration denied at the airport. Obliged to buy a new ticket. How can I request a refund?

I bought airline tickets for 4 passengers from Expedia to fly from Singapore to Thailand through Thai Lion Air (subsidiary of APG Airlines). Two days after buying the tickets, I called Thai Lion Air for a flight change for 2 of the passengers. Tickets are now separated into 2 sets of 2. The first pair flies on December 1, while the second pair flies on December 3. I made the necessary payment and confirmed that the transaction was made with my credit card. The confirmation and the receipt were sent to me by email for all entries (2 itinerary games).

On December 1, the 2 passengers were denied check-in, since the airline's system reflects that it does not leave because the payment was not made. The couple was forced to buy a new set of tickets that cost twice as much as the old tickets. I contacted the airline and they informed me that their system was not presented and that they could not proceed with the refund. The ticket sales staff of the airport issued us a record that indicates everything that happened from the purchase until the day of the flight, but its system in the headquarters shows otherwise.

On December 3, the last 2 passengers were able to board the plane without mishap.

I contacted my credit card company and Expedia about this and both parties stated that all payments have been made. I have filed a complaint by email attaching each piece of supporting documents that show that the passengers showed up but the airline does not respond.

I want a refund for new tickets that cost twice as much. What can I do to recover the money? It felt as if the airline was deliberately trying to cheat this trick.