They must change their spiel and caller ID every couple of minutes. My caller ID just said "Out Of Area," which is shorthand, to me, that it's a scam or telemarketer. Now in my permanently blocked file.
BTW, I do have the Panisonic call-blocking phone--it works great, but it only holds 50 blocked numbers. HOWEVER, it does hold about 3500 numbers in the phone book, so when I sometimes just save a telemarketer's number, change the Caller ID from "Out of Area" to "Telemarketer" and then when they call back, I know not to answer it. And they DO call back, the *&^%%^s.
First, I hope these people didn't scare your son.
Second, and most importantly, it is an illegal collection tactic to threaten arrest for not paying a bill. Please file a complaint with the Attorney General of your state, and a complaint with the FCC.