I Initially tried to make a purchase from Paypal (using an AmEx card) which did not go through (and was unable to use alternative payment method as the checkout page was giving a error like "Reference ID" missing. Closed my browser (Chrome on Android KitKat) and logged in, This time my cart was empty so added JoomSocial Professional Edition (149 Billing amount, no duplicate seen) ...
But after the payment I was charged twice i.e. to payments of $149 and two purchases were seen in my download area.
Could you please Refund order #15519 ASAP
I just verified and everything is fine on our side. I will send you an email with an attachment that show the status of that transaction just in case you need to contact your bank.