Harassing phone calls, without telling WHO they represent, on a daily basis!

I finally got fed up, and called them back, and got a guy called "Billy" who simply refused to even tell me who they work for, or the name of the company, and proceeded to hang up on me!  I called back, and got the same jerk, and asked what is your company called?! He started yelling at me, and before he could say anymore, I hung up.  I thought there were laws against this kind of threat tactic, harassment, and rude, obnoxious behavior, from bill collectors!!  I was not even the person they were looking for, and they took my number off their list, but, they have NO right to be so rude and unprofessional, when harassing citizens-- especially when they are at fault, and it's their mistake!!