You can try complaining to the Better business Bureau or the attorney generals office or whoever handles consumer complaints in your state- When a company like Dell gets notification from the BBB or an AG, they definitely dont want to be on the wrong side of that one.
I once had a company that basically wouldn't do what they were supposed to do; never returned calls, emails etc... As soon as I made the complaint to the BBB, I received a phone call within a few weeks and the company took care of what they were supposed to.
Its definitely worth a shot- especially if they never even notified you that they cancelled the order.