Last week I booked a ticket on continental.com using a voucher I received from a much-delayed flight a few weeks ago. The voucher states it is valid for $25 off a $75-$199 ticket, up to $100 off a $400+ ticket. When booking, the website gave me a price with voucher of $0, and I finished the booking, no credit card number required, and I received the itinerary email saying my purchase was confirmed.

I figured this was too good to be true, but perhaps they were so sorry for our miserable 4 hours stuck on a broken plane at the gate that they recoded the vouchers for free flights.

I never got the eTicket Itinerary and Receipt. A few days later, I received an email from the electronic support desk asking me to call as there had been a delay in ticketing the reservation.

I called and was told there had been a mistake, and that they could now ticket it for $692 minus the $100 voucher. The problem is that $692 is today's fare, and it was significantly less a week ago when I booked it. Since I booked the ticket at $0, I don't have any proof of what the price was, if they're not giving it to me for free.

I'm willing to pay for the ticket, but at the price at the time I booked it. What do I do?