Turkish Airlines Ticket Change Issue

I purchased a one-way ticket from SAW to Edremit for 18.11.23 from Pegasus and a return ticket to Istanbul Airport for 20.11.23 from THY. Due to weather conditions, the flights were canceled, and Pegasus refunded the ticket. However, since I couldn't travel to Edremit, I asked THY to credit my ticket. During my call with customer service, they informed me that since I bought my ticket under the Ecofly category, they could only refund the 12.42 ₺ airport tax and couldn't credit the ticket. They mentioned that tickets bought from the call center cannot be canceled or changed. I explained that I purchased my ticket online and did not receive such a warning. The customer service representative insisted that this policy was indicated, but I am not convinced. Despite researching on their website, I couldn't find clear information. I am requesting that my ticket be credited at least 16 hours before the flight, not canceled. I do not accept that this cannot be done.