Turkish Airlines Flight Check-In Not Working

I am unable to check in for my Turkish Airlines flight, even though there are more than 12 hours remaining until departure. The system keeps showing an error. The last time I encountered this issue, despite being at the airport an hour before departure, I was denied check-in and was told that I was late, causing me to lose my ticket. How is it ethical to oversell tickets and then shut down the system? Today, I have an international flight, and I am worried I will be forced to pay an extra ₺50,000-₺60,000 for a new ticket again. I urgently need a response to resolve this issue immediately.