Gift Cards

I have 4 Dell Gift Cards that have no expiration date on them, however when I try to use them towards a new purchase I am being told that Dell no longer accepts gift cards.  These are NOT promotional gift cards but ones that were purchased.  How can you refuse to honor gift cards that were paid for?  I have gone around in circles with sales and customer care for hours and everyone just transfers me to someone else and eventually the call gets dropped.   I want to buy your products and use the gift cards to pay for part of the order, how can this be done?