Is it possible that you submitted the order twice?
I can see two identical purchases with your e-mail, 3 minutes apart... so there's no wonder it got billed twice - there were also two license files delivered (they shouldn't be completely identical if you compare them byte by byte - the customer number is different, for example).
I'm sure it's possible to cancel&refund one of the orders. I'd say try to contact Digital River, as suggested by David, and explain them the situation. If it won't work, please write to support@avast.com.