When you say you couldn't understand the company they gave you do you mean you couldn't make out the name of the company because they didn't pronounce it clearly? Mumbling deliberately like that is a fairly common tactic of criminals who try to impersonate debt collectors. They want to sound official but they either don't *have* a business name or they are a business that wants to keep a very low profile... to law enforcement agencies who might bust them.

You probably ought to file a report with your state attorney general. Perhaps notify your local law enforcement, too.