i changed my itunes password and got charged

You may have received a temporary store holding charge, that is applied when you add or change card details on your account or can happen when you change other details (e.g. name, address) - the 'charge' is to check that the card details are correct and valid and that it's registered to exactly the same name and address as on your iTunes account, your card issuer should remove it from your card within a few days or so.

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

Was the password the only thing that you changed ? You've checked your account's purchase history : See your purchase history in the iTunes Store - Apple Support?