i bought an App from the app store and more than the stated amount was deducted from my bank account

Go to https://reportaproblem.apple.com, select the transaction and report the problem. If that does not help, then you can use this link to contact iTunes support to ask your question. iTunes Store - Contact Us - Apple Support

Get help with an item purchased from the iTunes Store, App Store, Mac App Store, or iBooks Store - Apple Support

If there were 2 charges against the credit card and one was very small, it was likely a charge to validate the credit card. That charge will be dropped.

How much more was deducted? In the U.S., Apple charges sales tax at the rate for your local address.