Turkish Airlines Flight Ticket Discount Code Issue

I am an Erasmus university student currently abroad. With the code we received through the THY-national agency agreement, we are entitled to a discount on THY flight tickets and extra baggage allowance. I used this code for my return flight from Porto to Istanbul on February 29, 2024. However, I urgently needed to change my ticket date and wanted to cancel the ticket and purchase a new one. But the code is invalid for my new ticket, even though I haven't used a flight with the code. I wrote to THY about this. In response, I received information related to 'MEB Scholar,' which is irrelevant to me. I am not an MEB scholar. I wrote again, stating that incorrect information was provided and that my message was misunderstood. But still, no resolution. I risk not finding a ticket because they sell out quickly. As a last resort, I am writing here to resolve my issue. I hope my problem, which has become an unresolved situation, will be clarified and I will receive a new code.