Q: I need to refund my book, but it was not accepted.

We are fellow users, we won't know why iTunes Support won't refund you - but all purchases are considered final, refunds are generally only given for things such as items not working (e.g. song or film not playing), or not as described e.g. (app not having functionality described on its description page, book in wrong language).

Did you not download a sample of the book first ?

Depending upon how you tried requesting a refund, try the other link : http://reportaproblem.apple.com or http://www.apple.com/support/itunes/ww