If when you process your order the postcode does not match the billing address, your order is unlikely to have been successful. Although the payment will look like it has been taken please be assured it hasn't and should disappear from your statement within 24-48 hours.
The most common reason for this is due to the billing/credit card address not matching the address registered with your bank. Please make sure all your details match exactly as your registered bank before attempting payment again.
If the issue persists, you may try the alternative Paypal payment method with your credit card.