Issue with Turkish Airlines TK2660 Flight Ticket and Check-In Process

I had a challenging experience with my Turkish Airlines TK2660 flight from Istanbul to Sivas on 22.07.2023. I purchased my ticket in May, but on the day of the flight, I encountered several issues. Although the flight was scheduled for 17:05, I attempted to check in online around 13:00, but the system displayed an error. When I arrived at the airport at 16:05, I was informed that the seats were full and I could not board the flight. They offered me a compensation of 100€ and a seat on the next available flight. The airport staff made passengers run from one place to another. Eventually, I was able to board the flight because some passengers were late. If they had arrived on time, I would not have been able to travel despite having paid for my seat. This situation is absurd. The response I received stated that they oversell tickets in case some passengers do not show up and that I was late for check-in. They mentioned that check-in should be done at least 45 minutes before the flight. I tried to check in twice, once 4 hours before and once exactly 60 minutes before, but both attempts failed. When I went to the airport counters with 60 minutes left, they told me the seats were full. I managed to board the flight thanks to the no-shows, but if you plan to travel with Turkish Airlines, be aware that you might not be able to board even with a paid ticket. (Three other people were in the same situation as me.) If you have an urgent trip, it should not be with Turkish Airlines. They responded to my feedback without fully reading it, misspelling my surname and stating they could not offer compensation upon my request. (I did not request compensation in any sentence of my feedback.)