Turkish Airlines Refund Dispute - Incomplete Ticket Cancellation

I bought a ticket for two people from Turkish Airlines, and it covers both the departure and return flights. My friend couldn't catch the flight from Istanbul Airport to Gaziantep on March 9th. On March 10th, I tried to cancel the other person's ticket for my flight from Gaziantep to Istanbul (PNR: WMSHQN). The mobile app said I would get a refund of ₺1245. I went ahead with the transaction, and the ticket was confirmed as a single ticket through an SMS notification (PNR: SLYS5Q). Unfortunately, a refund was not issued. When I reached out to customer service, they informed me that only ₺139 would be refunded. I raised my concerns and completed a form to request a refund, providing a detailed explanation of the situation. The following day, the notification made it clear that no refund would be given. I want my money back right now. I'm really curious about how Turkish Airlines is saying they didn't process my cancellation, yet I somehow ended up with a new PNR. Can someone explain this to me? They can sell my unused ticket to someone else. Here's my membership number: TK432188188.