I Was Unable to Change My Turkish Airlines Flight Ticket Despite Having the Right

I purchased a student ticket for the dates June 6, 2023, IST-AUH, and June 13, 2023, AUH-IST. My package included the right to make changes. When I wanted to change my return ticket, I contacted customer service. They informed me that I could make the change with Anadolu Jet if my package was downgraded. However, when I selected Anadolu Jet in the app, I encountered an error in the fee calculation. I explained the situation to customer service again and they confirmed that I could change my ticket after downgrading my package. Despite this, I received a system error and was told to call back after a long wait. When I tried to change the ticket again through the app, I received a warning that I did not have the right to do so. When I called customer service, they told me I did not have the right to make changes. Even though I mentioned it was a student ticket, they insisted it was a normal package. Despite having 40 kg baggage allowance, the ticket appeared as normal. When I called again, they said I had the right to make changes but couldn't complete the process due to a system error. Despite multiple calls to customer service, I couldn't resolve the issue. While heading to Abu Dhabi, I went to the THY office at Istanbul Airport and explained the situation. They said they could change my ticket but encountered the same error. I mentioned that I wanted to use my one-time free change right for students, but they couldn't do it either. Shortly before my flight, they suggested I call customer service again, but I didn't have time. I was sure I would get the same result even if I called because I had tried multiple times. I also spoke with customer service in Dubai, but they couldn't change my ticket either.