Our payment system is heavily tested to ensure the correct amount is charged and your transaction is completely secure. We use Stripe to process all payments because they are Level 1 PCI Compliant, which in simpler terms means, we offer most secure possible checkout experience.
Despite all measure we take to ensure cards are charged properly, there is a scenario where your card may appear to be charged twice when, in fact, it has not. Generally, this happens when our attempt to charge your card initially fails and then a subsequent attempt succeeds. Certain banks report a failed charge attempt as a "pending" transaction which makes it appear as if we charged you twice. After a few days, the pending transaction should be dropped by your bank and you will see we only charged your card once.
If you ever have questions about billing, do not hesitate to contact us.