Refuse to refund double payment

I am bitterly disappointed at nu metro, their self help Kiosk processed my transaction, and then it did not print my tickets. I went over to the other side and told the guy what happened, he insisted that I did it wrong the first time, and said I must try again. The transaction went through again but this time I got my tickets. My bank does not show transactions immediately, but 2 days later it showed the transaction twice. Nu metro refused to reverse the transaction and said I must give them a 7 day statement. Eventually after 7 days I gave them the printout and informed them that is all my bank could give me. They then said it is going to the refunds department, when I followed up a few days later, they are insisting on another statement even though they traced both payments. This is a huge inconvenience, I didn't ask for my money to be taken twice. This is going to cost you a lot more than what you owe me, there are many cinemas out there.