Not only am I glad to hear you received your due amount but also that you had the discipline to keep your cool and not sink down to his level. Unfortunately, like the debt collector mentioned, this is not uncommon. Sadly enough. The sad thing also is that an encounter like this often causes unseen damage by word of mouth from this guy who will likely be venting to his friends and colleagues how "unprofessional" you were. Hopefully that is short lived and won't affect you in the long run. Although...
Years ago I was production artist for a screen printer in my home town. We handled a lot of imprinted products directly to small business on a regular basis but we also did a lot of contract printing for resellers. One particular client was particularly nasty to deal with. The dreaded nightmare customer. He never had anything good to say, was very picky beyond accepted margins, complained about pricing, about product quality of the substrates we printed on (of which he specified), and more. I had to give credit to my boss, Jeff, for keeping his cool in front of this jerk but I did see the after effects this bastard had on Jeff's nerves when the guy left the shop.
My boss put up with this guy for almost a year before finally deciding to give the guy the boot. Rather than tell him he wasn't interested in doing business, Jeff sent him a form letter saying that due to increases in material costs, yada yada, we would be going up in our contract pricing schedule for the new year. He padded the prices to a believable point but one he knew this guy wouldn't accept. The fall back was that if for some reason this guy persisted in using us, the inflated price would pay for the agitation. Basically a win, win situation.
As suspected, the guy bitched and complained about the rise in rates and said he couldn't see himself continuing to do business with us. Victory! We were rid of a thorn in the side. We thought we'd never hear from this guy again so it was a surprize when over the next several months we had more than a couple new customers come in telling us we were recommended to them as "the best in the area" by... the thorn in the side.
Who would have thought?
"If you didn't learn something new today, you wasted a day."