Turkish Airlines - don't trust them!

Booked an overseas trip on Turkish Airlines. Specifically chose them because there was a good chance I'd need to change my return date and they advertised a low change fee. I had to book early in order to obtain a Schengen visa, but two weeks before the trip, I requested a change of date for my two-leg return flight. TA in SA didn't take my calls and didn't reply to my emails, so I contacted their head office in Istanbul. Their customer service people weren't helpful and told me I'd have to pay far more than the full cost of my original ticket, just to change the return date. They said that similar fee classes weren't available, even though I could see plenty of availability myself on their own website. I lodged a complaint and was promised an answer within a day. One day become many days and then a week and I was getting no answers at all. I even complained to Star Alliance, of which TA is a member. They didn't have much to offer either. When I left SA, I went into the TA office at CPT airport and complained again. Although they were doing their best, TA head office were uncooperative. When I arrived at my destination in Spain, I again went to the TA office to lodge a complaint. The lady there was very surprised by what TA head office had told me. She looked online and found plenty of availability in similar fee classes, so happily changed my return date with the change penalty in line with what TA's website had stated when I booked. The same day I arrived in Spain, there was a new email from TA head office, basically saying that no similar classes were available and that all their terms and conditions when I booked reflected this, and that I should pay the US$900 or so to change the date. This was untrue as none of the info they claimed was on their website was there when I booked. I checked repeatedly. They tried to deceive me and I will be taking it further, so others don't get deceived and have to experience the same unpleasantness.