FlixBus Changed Our Reserved Seats And Charged For Refund

We bought our tickets by explicitly choosing our seats, and we bought the tickets because we were able to reserve 1A and 1B seats. 26 days later, we got an email saying our seats were changed to 15C and 15D. I started to chat with an Expert and he said “We did not pay for it”. While booking the ticket and choosing the seats, there was not any additional charge (we would pay if there was), so that’s not my problem and fault that Turkish Airlines did not charge. We wanted a refund because of the change of the reserved seats, and we charged with “processing fee / 123TRY per person”, so they refunded minus the processing fee by saying “because you did not pay for the seats”. Because of THEIR BOOKING SYSTEM FAULT, we could not use our bought tickets and CHARGED for a refund.