Turkish customs on educational materials (Istanbul)

I need help!
Turkish customs is holding my University books. I don't understand why they would take them. They're just for my study. I can't resell them. And I can't buy them in Turkey.
I had never used FedEx before. I had always had my books sent US Mail and now that I have used FedEx my books have been stopped in customs.
FedEx is holding them in their warehouse and charging me. In the end with taxis and all the taxes and fees it will cost me about 900TL to get 240USD in books!
I can't believe it!
Does anyone know the customs rules on educational materials? I have googled it and can't find a definitive answer.
Sad days, indeed! I am a poor University student teaching English part time till I finish my degree :( This is a pathetic situation to be in but I'm in it!
Does anyone have any advice??
Thanks,
Callie