I went to the Gold Flight Connections desk in IST who sent me to ticket sales beside him.

They told me it would be €150 to change and they couldn't do any better.

I went to the lounge and asked there. Unfortunately dealt with the rudest agent I have ever come across who said since I've already changed my ticket it was impossible to change my ticket again and I'd have to buy a new ticket. My "change" was a misconnect due to a delayed Turkish flight. I tried to explain this and said it should be around €150 according to ticket sales. She just threw my boarding card at me and turned around to face the wall refusing to talk. Was bizarre behavior.

Anyway in the end just stayed on original flight and TK put me up in hotel with dinner and breakfast. Seems like it would have been in their interest to put me on earlier flight but sure.

I still can't get over the agents behavior. Never seen anything like it.