Why Turkish Airlines Charge Extra for Refunds?

I bought a round-trip ticket from Turkish Airlines that was fully refundable, but when I went to get my money back, they took out 99% of the price of the ticket. I don't understand why they charged extra for the option to get a refund when I bought the ticket. Now, they're only giving me back 1,500 TL for a ticket that cost me 24,000 TL. To make matters worse, I had already paid an extra 400 TL for the option to get a full refund. When they offer full-refund tickets, I don't understand why Turkish Airlines insists on these huge fees. I want a full and quick refund of the ticket price.