Turkish Airlines Denied Me To Board Due to Overbooking

On January 28, 2024, I had purchased two tickets with the PNR code SU25IZ for the THY Anadolu Jet flight TK7260, departing from Istanbul Sabiha Gokcen to Adana Sakirpasa at 09:35. I left my house two hours early and arrived at the airport at 08:20. Due to weekend congestion, I waited 10 minutes at security before entering. To avoid any issues, I completed my online check-in at home on January 27, 2024, around 18:00. My wife and I were assigned seats 26E and 26F. Despite being in line at the counter about an hour before the flight at 08:40 and informing the staff that we were there to check in our luggage for the 09:35 Adana flight, we were directed to a long queue. After a long wait, we were redirected to a shorter queue, likely at counter H-20. The staff delayed us there, and when it was finally our turn, the attendant informed us that we couldn't board due to overbooking, even though we were in line and the counter was open. The attendant claimed we were late and had less than 45 minutes before the flight. Despite our protests and showing our check-in details, the system was closed, and we were told we had no right to board. The attendant admitted there were no seats left and that they had the right to oversell by 10%. Even though I showed our seat numbers, I learned that our seats were given to others. While luggage check-in was still ongoing, I was told my ticket was void. As a government employee needing to return to work the next day, I was told to speak with the ticket sales department. At the ticket sales department, I was offered a flight at 02:00 from Istanbul airport, but with an additional charge of ₺3,500 for two tickets, further inconveniencing me. When I requested a refund, I was told only the tax amount of ₺103.77 per ticket could be refunded, which I had to accept. This was my first time experiencing such an issue on a flight. I request that my grievance be addressed and resolved.