Comment Department of Fair Trading (or US equivalent) (Score 1) 593
I had similar problems with Dell Australia recently, and after a month or so of trying to play nice I looked up the location of their Australian office and contacted the Department of Fair Trading in that state to ask them for assistance. They took over from there and within a week I had the Executive Customer Escalation Manager for Dell Australia ringing and emailing me (and leaving me her direct email/phone number), apologising profusely and trying to get everything sorted out.
I don't know if a similar government regulatory body exists in whichever state Dell US are based in, but do a little research and if one does exist, ask them for help. Make sure you let them know eveything you've tried so far, and include any and all documentation to support your claim.
Good luck!