Go to BudHibbs.com. It gives you all the info on how to deal with these people. You do have to pay monthly on your bills but you can get rid of collectors.
I had my cell phone company set up a blocking application on my phone and these people still got around it. The cell phone company said that fraud schemers often will use technology to disguise the number they are actually calling from so that you can't block the number. My cell phone company said that the only way to truly figure out who is calling and where they are calling from is by going to the police and having them trace the calls.