A payment could have failed for a number of reasons. In most cases, you will need to speak with your bank. If you have any questions about your payment, note the Payment ID from your email receipt and contact the team either at firstname.lastname@example.org or by submitting a ticket here.
If you have made a purchase with your Credit Card, haven't received the item, but are still seeing a charge on your credit card statement–this is most likely a pending authorization. All credit card payment providers have an authorization period to allow a charge to be made to a customer's credit card. The authorization period will end after a certain amount of time. Once the period ends, the hold will be dropped from your card. The length of the authorization period depends on your credit card payment provider. You could end up with a pending authorization if the asset has already been purchased before your order had time to complete.