Knetbooks Kept my book after charging me for incorrect book sent back after semester rental. Internet

I rented a book at the beginning of the semester and had no problems all semester. Then when I went to return the book I sent them a book to send to Amazon and Amazon's book to them. I then left the country and was made aware of it through email but did not realize the severity of the situation. After recieving it, they gave me 5 day's then charged me the full price of the book at 290$. Then gave me 3 more days to pay for shipping to get my book back. After that point they kept the book and now a month later after 3 calls, 45 minutes on hold for each, I am not able to get my book back. They own my book after me not claiming in a few day's after a simple shipping mistake. The worst customer service I've ever worked with and horrible ethics in getting the issue resolved. They now own my book and charged me for the book and I am left to correct the issues with amazon and eat the cost. I will never recommend or rent/buy a book from this company or their larger company.