Turkish Airlines Flight Seat Issue on Van-Istanbul Route

On January 25, 2024, I purchased a ticket for the Van - Istanbul flight. I paid an extra fee to reserve two-person seats and also generated my boarding pass. At the airport, during boarding, the attendant informed me that the aircraft had changed, and therefore, the seat arrangement would be altered. Despite seeing empty two-person seats on the screen and informing the attendant, I was placed in three-person seats with the response 'there's nothing I can do.' Now, despite paying an extra fee and being an Elite Card member, I don't understand why I wasn't given a seat in the available two-person seats. When I reported this to the THY call center, I asked them to create a complaint record, but I received the response 'we can't do anything.' While there are no issues offering all kinds of services and charging fees during ticket sales, when it comes to complaints, the call center says they can't see the seat layout of the aircraft. I received the same response when I called before the flight took place. Is this the customer satisfaction understanding of such an institution?