If it's this ibook Breaking Bad: Alchemy then you can't read it on a computer, the requirements for that ibook on its description page says that it can only be in the iBooks app on an iPad (most ibooks can be read in iBooks on an iPad, iPhone and iPod Touch, only some DRM-free ibooks can currently be read on a computer).
If you haven't got an iPad then ttry the 'report a problem' link from your purchase history : log into your account on your computer's iTunes via the Store > View My Account (Store > View My Apple ID on iTunes 11) drop-down menu option and you should then see a Purchase History section with a 'see all' link to the right of it ; click on that and you should see a list of your purchases ; find that ibook, click the arrow to the left of it, click the 'Report a Problem' button
and then the 'Report a Problem' link on its line :￼
and select 'inadvertently purchased' as the problem and fill in the details (iTunes support should reply within, I think, about 24 hours).
If the 'report a problem' link doesn't work (it's been taking some people to this site on a browser instead of showing a form in iTunes) then you can try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page.