Turkish Airlines/Anadolu Jet Ticket Change Issue for İzmir-Ankara Flight

I purchased an economy class ticket from THY/Anadolu Jet for my son Um**** K***** for the İzmir-Ankara flight on February 22, 2024 (Ticket No: 2352217699723). Since my son is a student abroad, we also secured a ticket from Sunexpress for the Milan-İzmir flight. However, due to a change in the exam schedule at his school, we wanted to either open the tickets or postpone them to a later date. Sunexpress approved our request to change the ticket to March 21 by paying the fare difference. However, despite our applications both by phone and in writing to change the February 22 THY/Anadolu Jet ticket to March 21, we did not receive a positive response. In response to our written application (THY Complaint No: 10369670), it was stated that attention should be paid to the ticket's characteristics and that the transaction should be carried out accordingly. It was also emphasized that changes should be made through the company's online transactions.
I find it difficult to understand how a person is penalized for not being able to fly on the relevant date due to reasons beyond their control in extraordinary circumstances. While Sunexpress accepted the change by charging a penalty fee since there were more than 72 hours before the flight, why does THY/Anadolu Jet not accept the change in the same situation? Doesn't this create a grievance? For example, when THY/Anadolu Jet delays a flight due to reasons beyond their control, such as weather conditions or air traffic congestion, can the passenger say, 'I want to fly at this time, I missed my appointment, I missed my business connection'? Although it is said that 'international civil aviation rules' apply, these rules generally favor the rule-makers and disadvantage the service recipients. I request clear and precise information regarding our ticket and an explanation as to why changes cannot be made despite there being more than 72 hours before the flight. I am also reporting this situation to consumer associations and unions.
For a student, being forced to pay for a flight ticket they cannot use is quite unreasonable.
Ce**** K*****
A Concerned Parent