Barnes and Noble Cyber Monday $20 Gift Card Scam Internet

On Cyber Monday I received an email from Barnes and Noble offering a $20 gift card with the purchase of up to three of the specified Nook devices if paid for with a Mastercard.  I ordered three Nooks that were on the list and expected to receive three gift cards.

When the cards had not come by December 7, I called customer service and was told I would receive them by December 14.  On December 17, I received two, not three, $20 gift cards.

On December 28, I called B&N and asked for the remaining $20 gift card.  I was told that the offer was good only while supplies lasted and I must have received the last two gift cards!  I think that this is a blatant scam by a major retailer and the persons involved should be ashamed of themselves.
 
My three nooks were ordered in the morning and I doubt very much that they had run out.  Also, the way the ad was worded, it sounded like the offer was good as long as the supply of nooks lasted, not the supply of gift cards