Just log a request with App Store customer service, they are generally very helpful and friendly types. It may just be you need to show them some copies of statements if they are having difficulty reconciling from their side.
If you want to go the bank route, the codeword you want to use is "chargeback"...(or "Visa Debit Chargeback scheme" in it's long form). If you are talking to a muppet on the other side of the world, then this may need to be combined with codeword "escalate" (otherwise known as "can I talk to your manager"). ....
