Not sure what reasons they have for locking his account, but I'd be willing to bet they didn't look into the matter over the phone because of the guy's attitude. Contrary to belief, phone support reps don't have to put up with people yelling and screaming at them. I've worked a number of call centers over the years, and in all of them, the reps are told, if dealing with an abusive customer, to politely end the call and hang up. It's their job to help you, yes, but it's not their job to be your whipping boy.
And there's no sense whatsoever taking your anger out on a person who had absolutely nothing to do with your issue to begin with. Did this idiot really think that someone maliciously double-billed his account? It's probably just a computer glitch or a clerical error, and I imagine had he been more sociable about it, they would have been happy to clear it up.