This happens hardly ever, but if it does happen to you it's because -
When you pay using PayPal, we receive a notification from PayPal to advise us if the delivery address provided is confirmed on your PayPal account.
If they advise us that the address provided is unconfirmed, we need to receive confirmation from you in writing to allow us to send your order.
Simply reply to the email we send you to confirm that the delivery address is correct and we'll dispatch your order as soon as we can. If we don't get a reply to the email within 7 days, unfortunately we'll have to cancel your order and process a full refund.
When you pay using your credit/debit card, various checks are carried out to protect your card from fraudulent activity.
The most common check is to ensure that your billing address accurately matches that held by the card issuing bank. If some of the details match, but not all, we will email you to confirm. If none of the details match, then your order will be cancelled and refunded and you will receive an email to confirm this.