zmatrix, don't sweat it, man. We've all been there plenty of times. The fact of the matter is, you "won". You got the DVD, and if the losers that worked there didn't want you to have it that badly, they must have just been furious to see you walk out with it.
For what it's worth, writing corporate sometimes does help. I've gotten managers fired before, not at BB, but other stores, for situations very similar to yours. Just track down as many upper management, corporate, VP, etc. email addys as you can, and CC all of them about it. Make sure to give names, times, etc., and spruce up the story a little bit, threatening to post on every BBS, newsgroup, etc. The state of customer service these days is completely inexcusable. All you were trying to do was take them up on their own company policy.