Johanna--
Once you get the address, you need to send out the DV letter right away, as soon as possible. The law requires them to stop all collection activities until they have satisfied the request for validation. This includes filing in court. They cant take any action on this account legally once they receive your letter, until they properly answer it. I am going through something similar right now in that we sent out some DV letters last week, and already I have one CA calling me anyways....
But dont let the threats scare you--they make it almost sound like a hollywood movie sometimes, "my people will be at your house within the next half hour...." lol It is just a scare tactic. They cannot have you arrested, they cannot send people to your house, or your work, or to your parents house, etc etc etc, all of that is illegal. The next time one of them tells you this, maybe you should consider calling his bluff and telling him to get right on it so you can gather the evidence needed to sue him for violations of the fdcpa...companies like these operate entirely on the premise that the debtor on the phone has no clue about the law or their rights...if you show them otherwise, they often sing a very different tune in a hurry.