Turkish Airlines Flight Check-In Issue for 18.08.2023

I had a ticket for the THY flight on 18.08.2023 at 16:20. Despite arriving 1.5 hours early and joining the check-in line, the crowded and shared counters for all flights caused me to reach the counter at 15:30. As I hadn't done online check-in and it was past the last 60 minutes, they informed me I was late and couldn't board the flight. Approximately 10 other passengers faced the same issue. The flight was delayed to 16:40, but the ticket issuance time was considered for the last 60 minutes. After much effort to resolve our issue, we were escorted to the gate with our luggage, being told to wait on standby. We reached gate 119 at around 16:35. After all the passengers boarded, they closed the glass door at 16:50. They then told us, six people, that we couldn't board. My questions are: 1. How did you sell my seat to someone else within 10 minutes? 2. We requested a review of camera footage to see how long we waited in line, but they said we should have checked in 3 hours before for international flights. 3. I had purchased extra baggage online, but they didn't refund it, stating it had to be done before the flight time. How could I have done this when I still had a chance to fly until 16:50? Please open separate counters for each flight to see who really arrives on time. Also, two other passengers had online check-ins, but they were still made to run around for an hour because it was past the last 60 minutes.