I'd have been triply furious. I've sworn off rebates completely, and I'll certainly think twice before buying UMAX again. In fairness to them, most companies hire outside contractors to handle their rebate redemptions, but considering that my only experience with UMAX customer service has been with their rebate department, they need to maintain tighter standards over their careless, clueless contractors. Rebates are an incredibly popular way of discounting computer stuff. Unfortunately, that's unlikely, as stores love to promote rebated prices as it makes their prices seem cheaper, and few consumers can resist what seems to be a good deal.
Consumers are notoriously apathetic after the fact.
I fear the only remedy is regulation. I'd like to see some standards imposed. All rebates should have similar rules and regulation, and there should be appropriate penalties if the corporation offering the rebate violates those rules. There should be minimum standards for hold times and service hours. Photocopies of receipts are acceptable.