In addition to the other points made, here are the rules of reuse on unused tickets or vouchers:

The tickeholder has one year from the ORIGINAL date of issue in order to rebook the ticket.

For example: Lets say you booked a reservation on 12/20/05 for travel on 7/6/06 and paid 500.00 for the ticket. Something comes up and on 2/1/06, and you call Delta and cancel your ticket. They will inform you at that time, that you now have a credit for 500.00 toward the purchase of another ticket, and need to rebook by 12/20/06 (one year from original date of issue). You can see by this example that the original date of issue is the important thing. The original date of travel, and even the date you CANCELLED it, do not matter to Delta, or ANY airline for that matter.

What they will NOT say 'you have until the end of the year to reuse this ticket (or voucher)'. There is absolutely NO way that this was said, I can guarantee you that.

The reason the person couldnt locate the 730.00 credit is that on the EXACT date of expiration, it purges from their reservation system. So even if you called them on 12/17/06, they are going to say they can't find it because, technically, it doesn't exist anymore.

I am sorry to inform you that in this instance, you are completely and utterly 100 percent in the wrong.