Is the system requiring a bank card? If so, it is most likely a security issue. I would call Apple Care for your country and ask help in determining what the issue may be. It may be that your security questions need to be reset.
The $20+ for the Pages app would normally be taken from the credit balance and $54 is more than enough to cover the sale.
Mac mini, OS X Mountain Lion (10.8.3), iPad 4, iPhone 5 (iOS 6.1)
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