Turkish Airlines Ticket Refund Issue

I purchased a round-trip ticket for two people from Turkish Airlines. My friend couldn't join the flight from Istanbul Airport to Gaziantep on March 9th. On March 10th, I wanted to cancel the other person's ticket for my Gaziantep-Istanbul flight (PNR: wmshqn). When I attempted to do this on March 9th, the mobile app indicated that I would receive a refund of ₺1245. I proceeded with the process, and the ticket was updated to a single-person reservation, confirmed via SMS (PNR: slys5q).
However, no refund was issued. When I contacted customer service and explained the situation, they informed me that only ₺139 would be refunded. I disputed this and filled out a refund request form to explain the situation. The next day, I was informed that no refund would be issued. I urgently request the refund to be processed. If Turkish Airlines claims that I did not complete the cancellation process, how did I receive a new PNR? They can resell the unused ticket. My membership number is Tk432188188.