why iTunes deducting money from my bank account.

It's called a "hold". That's how companies check if the credit card you provided is good. The amount will be credited back to your account within a few days.

About payment card authorization holds in the iTunes Store - Apple Support

Authorization Holds are not actually debits to your account, so no money is taken out. It is simply a hold placed against the funds. It has no affect on the balance used to calculate interest either paid or charged, just affects the balance available to be used (by a very small amount). Typically an Authorization Hold will be removed from the account within the next two business days.

Cheers,

GB