Turkish Airlines Flexible Ticket Issue for Istanbul-Miami Flight

On July 31, I added a Miami-Istanbul return flight to my previously purchased one-way Istanbul-Miami flight for two people from Turkish Airlines. Before booking, I called customer service and informed them that I would keep the return flight open and change the date later. They advised me to first purchase the ticket and then call them to proceed with the changes. I specifically chose the more expensive Flexible ticket, which allows changes without penalties, rather than a promotional ticket, as I knew the return ticket wouldn't be used and I needed the flexibility to change the date. I have done this process possibly hundreds of times before. To be cautious, I even took a photo of the selected flexible ticket during the booking process.

After making the payment, I received the ticket via email and noticed it was issued as a promotional ticket. I called immediately, within a minute, to request a correction. They directed me to a feedback form and initially claimed it wasn't their error, advising me to be more careful next time. I contested this, and now it's been 10 days with the review still ongoing. The flight is tomorrow, and the ticket will soon expire. I will have to forfeit the flexible ticket I paid for. I have never encountered such irresponsible and slow customer service. I am very dissatisfied with Turkish Airlines.