Delta

I am writing in hopes of getting an explanation because the customer care rep I talked to could not give me one. My parents, along with three of my relatives, were given credits of $349.20 each and were told by different customer care reps at differnt times on/around 7/28/2009 that they had till 7/27/2010 to use those credits toward another flight. When my parents and I recently tried to book a trip using those credits, I was told the customer rep made a mistake in both the amount and the date, and that my parents should have only gotten $149 credit and that they should've used the credit by 6/15/2010 (which now has expired). I'd understand if this was an isolated incident where one customer service rep made a mistake, but my relatives were told the same thing by different customer serv reps(!), so clearly it's not an isolated incident. My question then is did your policy/procedure change in the last year? or Did these customer serv reps all make the same mistakes? Either way, shouldn't Delta honor its word? I am clearly disappointed and puzzled by this because I understand the airline business is hit hard too by the recession, but my family and I were planning to spend $2000 to fly with Delta using those credits, and in your efforts to save $700 by not honoring your word, you lost $1,300 in business. Not to mention, my family and I will think twice now about flying with Delta in the future. It's not only unfair, it doesn't make business sense. My parents were offered $100 vouchers but more than that, I would like an explanation or for Delta to honor its earlier commitment.