@riasusama: This sounds like a payment failure. Have you checked the 'completed' tab of your orders and shipping page to see if it is there as a cancelled order?
In very simple terms, there are two points where an order may be 'cancelled'. The first is before the order is even accepted - usually an invalid card number or expiration date, insufficient funds, bad security code, etc. You could be having hundreds of those every day and would not even know it. The second is after the order has been accepted but has not yet been fully approved by the payment processor or the card issuer - generally flagged by one or the other's fraud detection algorithm and showing to you as 'pending'.
Digital downloads are often considered high risk transactions by these fraud detection algorithms.
However, even an approved transaction can be reversed. For example the card holder may have reported an unauthorized transaction.
