They basically reissue the ticket, canceling the original purchase and rebooking for you at the new, lower price. So the standard $50 change fee applies to most transactions, and it's only worth doing this if the price drop is greater than $50.

Was the first 'refund' you got done before midnight of the day after the ticket was purchased? If so, 'risk-free cancellation' applies, and there is no charge to cancel your ticket.