Cash Advance USA ACS Unauthorized Loan , Internet

I received a call at my parent's home from a "law agency" claiming that it was the last call for a debt owed to Cash Advance USA.  The loan was in the amount of $900, but no clear or exact figure was ever released, which brought to question the allegations even further.  I called them back, and the person on the other line sounded like he was on a cell phone.  Now, if you are calling from an official and professional office, wouldn't you be calling from a landline?  He looked up my account and said that I took out loans in the amount of $900, and that they had been trying to reach me to obtain a payment and settle the debt.  I have never made business with a company by such a name, nor have I taken a loan in that amount.  The man also claimed that they had information to prove my debt - my name, email, bank account, and social security.  I told him that this was not prove of anything and that I could furnish bank statements to show that I have never been in business with such a company.  He gave me "their" direct number (with an 805 area code, in northern Los Angeles).  I must have called more than five times, and every time it would ring for about a minute and then go off into what sounded like an outgoing fax dial tone.  I called the first agency back to let him know, and not only was his phone losing service, the man was also very adamant about me paying back the debt.  I told him that they had absolutely no prove that I ever took out a loan from them, and he continued to run down his list.  I told him that in a court of law, these items would not be considered prove of any transaction, and that they would laugh.  I also told him that I wanted these allegations in written form, to which he ended by saying: "okay, we will send you a written lawsuit in the morning."