Bank of America has this policy where you aren't liable for unauthorized transactions on your account so long as you notify them within a certain amount of time. Other banks might well have the same / a similar policy?

I guess the problem here is that you did authorize the transaction, but then you changed your mind. Might be a problem to try and sue them for false and / or misleading advertising, though, particularly given the international nature of the transaction.

One really does need to be careful about the circumstances in which one discloses identifying information (bank account details, social security number and the like). When I get notification of updates I check the authorized sites and make sure that I download from there. I use paypal whenever possible. I make sure my purchases are from authorized sites. I know this doesn't help you with respect to what has already happened, but hopefully this will never happen to you again.