zipzoomfly.com refuses to refund for non-shipment

placed order for hard drive with buy.com under order number 48301648 and they placed with zipzoomfly.com under order B4570710. I paid by American Express $78.53 and then zipzoomfly refused to ship this product and refunded only $56.75 citing restocking charge of $21.78. I live in zipcode 00907 which is a part of the United States and when this item was ordered, it included free shipping. Since this order was not shipped to me, I expect a full refund.