Turkish Airlines Refunded the PrimeFly Ticket Partially

I purchased round-trip flight tickets from Istanbul to Gaziantep for my family (5 people) on 31.10.2023 through Turkish Airlines' website. The departure was scheduled for 11.11.2023 and the return for 15.11.2023. I paid a total of ₺18,500 for these tickets and opted for the 'PrimeFly' category, which allows for a full refund within 12 hours, by paying an extra ₺300 per ticket (₺3,000 in total for 10 tickets). Later, on 06.11.2023, I canceled the return tickets through the Turkish Airlines website and booked new tickets for a different date. Despite canceling the 5 return tickets 9 days before the flight date and purchasing them under the 'PrimeFly' category, only 10% of the ticket costs were refunded to my credit card. 90% of the ticket costs were deducted. When I inquired with Turkish Airlines, they explained that if one-way tickets are canceled in a round-trip booking, such deductions are made. They stated that canceling the entire round-trip booking would not have caused any issues. Because I canceled only one way, 90% (₺8,000) of the ticket costs were deducted. If such a policy exists, why doesn't the system warn us that 90% of the ticket cost will be deducted if one-way tickets are canceled when recommending the 'PrimeFly' category, which allows for a full refund within 12 hours? If I had known about this policy, I would have canceled the entire round-trip booking and rebooked, avoiding any deductions. (After all, no discount is applied when booking round-trip tickets together.) After failing to get a satisfactory response from Turkish Airlines regarding the refund of the ₺8,000 I believe was unfairly deducted, I filed a complaint with the Consumer Arbitration Committee and have been waiting for their response for 1.5 months.