For those of you being harrassed, this website is GOLD re: getting rid of overzealous and illegal collectors (for instance, they can't come back to you 20 years after certain debts etc.).
Once on the website, Clark Howard has a ton of very helpful links to gov't agencies dealing with this sort of stuff.
Here's a link to the gov't agency for Fair Debt Collection practices. It works, I've used it myself. All I had to do was just MENTION this agency and I never got another call from a debtor that had been trying to collect a debt that had been legally paid 20 years before.
And here's their main website. Even if you legitimately owe the debt, they can't just abuse and threaten you, and you can be owed compensation if they go outside their rights.