Denied Boarding on Turkish Airlines Flight Without Any Reason

I purchased a flight ticket from Finnair to travel from Istanbul Airport to Tokyo, Japan. The flight was supposed to go from Istanbul to Helsinki, Finland, and then to Tokyo with a 5-hour layover. THY was supposed to take us from Istanbul to Helsinki, and then Finnair would take us to Tokyo. I have traveled to 12 different countries before and had Schengen visas for my European trips. I passed through passport control at Istanbul Airport as usual. When we reached the boarding gate, we waited for it to open. A THY employee named M******* F**** A**** asked those with a connecting flight to Tokyo to wait in a specific area. While waiting, he said he would take screenshots of everyone's passports and send them to the Helsinki police. As the flight time approached, 80 people with connecting flights were supposed to board, but only 75 did. The remaining 5 were Turkish citizens, including us, who were not allowed to board. When we asked for a reason, we were told that the Helsinki police had said not to let us board. When I asked why, there was no explanation. I mentioned that I had hotel reservations in Tokyo, had already paid for them, and even rented a car, but the officer still said he couldn't let us board. Despite having paid for the flight and having no wrongdoing, I was not allowed to board. THY knew I was being mistreated, took my money, but didn't let me board the flight. They didn't refund my payments without any reason. They made us wait at the airport for hours, ruining all my vacation expenses and ticket costs. Turkish Airlines, which is supposed to be a leading airline globally, is a disgrace in the aviation sector in my eyes. I will never buy a ticket from THY again and will take this matter to court. Even a local grocery store is more professional than your company.