Tracking Down Deadbeats

I have been busy chasing down customers who do not pay me. I have gotten several suggestions, which are great, but have yet to find a surefire way to actually get paid. Everyone I manage to get a hold of gives me the runaround - oh, we thought we'd paid you already - oh! I actually have one lady right now who is extremely upset with me because in some of the 30+ messages I've been sending her requesting payment, I'd mentioned that I was giving her name to other people as a customer to stay away from. She thought that I actually *owed* her the names and email of any of those people, so she was aware of who I was talking bad about her to. I explained to her that I am allowed to say anything I want, as long as it is true, and I don't have to tell he who I have mentioned her name to. I actually think that went a bit overboard - considering I have been trying to get her to respond to an email since December 17th, when she promised payment - All the excuses in the world non withstanding, she's been arguing with me via email now since last Friday, and I STILL haven't gotten paid. I wish there was a manual about these things....