Turkish Airlines Customer Service Canceled My Ticket Without Approval

I purchased a THY flight ticket for myself and my spouse from Agri to Izmir (with a transfer in Istanbul). I called customer service to reschedule the second leg of the journey, from Istanbul to Izmir, by 1-2 hours. The first representative I spoke with said I could change it for a fee of over 500₺ per person. I said I would think about it and call back. When I called back, another representative answered and told me there were no available seats for the change. I thanked them and ended the call. Later, I logged into the mobile app and saw that our Istanbul-Izmir flight had been completely canceled without our approval. After spending 2 hours on the phone with six different people, I had to pay 3,300₺ to buy new tickets. The status of my canceled flight is still unclear. THY caused us significant inconvenience. I want compensation for my loss.