Issue with Turkish Airlines Return Ticket Cancellation and High Fee Request

I purchased a round-trip ticket from Turkish Airlines for Vienna, scheduled for December 8-13. The night before the departure, six hours before the flight, I fell ill and had to go to the hospital, so I couldn't cancel my outbound flight. However, I still had my return flight. Two days later, I felt much better and traveled to Vienna with another airline. Today, December 13, when I was about to return to Istanbul, I was told at the baggage check-in that my return flight was canceled because I didn't cancel my outbound reservation. This is absurd. They said I needed to buy a new ticket, and if I didn't, I couldn't fly. I had no choice but to buy a new ticket, and they shamelessly charged me ₺9000. This seems intentional against passengers. I don't accept this. How could I call from the emergency room? I have documents to prove it. I want a refund. By the way, the plane was fully booked, but somehow my purchased seat was empty. I won't let this go. Turkish Airlines, I will never fly with you again. If I don't get my money back, I'll take this to both CIMER and the Consumer Court. Shame on you thousands of times.