Sometimes, a single recent purchase may appear on your credit card account as if it was charged twice. Usually, one of them is a pending transaction that is deposited on your bank account before it's finally authorized and charged, thus creating a second record in your transactions. Obviously, the second transaction then indicates the actual purchase and charge. A usual indicator for the pre-authorized order is that your bank account balance was changed only by the sum of a single purchase.
If you are sure that your bank account was charged twice for a single purchase, please, contact our support and attach the screenshots of the said transactions.