A less than reputable collection agency based in Washington State.  They purchase old uncollectable debts (more than 7 years old) or ones that have been paid, but the paperwork is less than perfect.  They try to intimidate the less savvy into paying a debt they legally do not have to, or one that has already been paid.  They will rattle off all sorts of case numbers and other made up BS.  To get rid of them:

1- ignore them (but they WILL keep calling- the reps get minimum wage plus a percentage of the amount they shake down)
2- say that you are recording the call and ask them to proceed with their request
3- ask them to put it in writing o that you can forward the information on to your attorney.

#2 works best. Let it go to the answering machine and then pick up so it keeps recording.  NOTE certain states require you to inform a second party that the call is being recorded. Like their collection scare tactics, the threat of recording their illegal and intimidating shakedown works wonders.

Also note that, if you want to be particularly mean, you can ask the caller if he/she has been paid lately, as the owner of this collection agency has been sued by his own current and former employee for non-payment of wages owed.  Snakes, all of them!