Airline spokeswoman Ashley Dillon on Saturday blamed a "technology glitch" for the duplicate billings to debit and credit cards.
She says the airline doesn't yet know how many took advantage of their "luv2like" promotion that gave customers who booked flights on Friday a 50 percent discount on certain fares. She says officials at the airline are working to refund erroneous charges.
Frustrated customers have reported waiting hours to speak to customer service reps.
The promotion was to celebrate the airlines' 3 million Facebook fans milestone.