Help! iTunes error message said try again later - instead I purchased 10 gift cards for my niece's christmas present!

Please help! I have written itunes support, who will get back when it is too late probably. My bank will not cancel my multiple mistaken purchases. It is not possible to call Apple about iTunes store purchases. My order does not show up on my account in iTunes, but 10 awaiting purchases shows up on my bank account. This makes my bank account empty! How can I cancel my order ASAP?