Issue with Turkish Airlines Customer Service

I purchased a ticket using my accumulated miles for a flight on August 25, 2023, with Turkish Airlines, but my flight was canceled. I wanted to use my free change right to reschedule my ticket. When I tried to do this through the app, all flights appeared to be fully booked, but when I selected 'buy ticket' again, I could purchase it by paying the fare. I then called customer service and explained that I wanted to change my ticket time. They told me that it was not possible, but they could refund my miles and the extra fee I paid, and that my miles and refund would be processed within 72 hours. They also mentioned that I could buy a new ticket for ₺1500. I had to hang up because I was busy at that moment. When I called customer service again, I spoke to someone else who told me that they could change my ticket time without any issues and kindly did so. How can your customer service provide such different levels of service? If I hadn't called back, I would have had to buy a new ticket. I purchase tickets from Turkish Airlines every week, and experiencing such issues is very upsetting. I request that necessary actions be taken.