Law and investigation dept us harrassing call for payment l0s angeles, California

I received a call today from Frank with Law & Dept Investigation Services.  Told him I could not understand him (Indian accent) so he then put Nash Brown on the phone.  I was told that there was a lawsuit pending against me for check fraud and theft deception for a cash advance I had taken.  I was told that I was sent emails regarding this account (which I have never received) and that EFT payments were declined by my bank and that I owed them $875 that had to be paid today.  I repeatedly requested info as to when these declines were made by my bank because I have nothing on my account and he would not provide me the info.  I asked when I had taken the loan and he would not provide info. Was told that if I did not pay today at least $500 with the balance paid in three weeks that I would be taken to court in CA and could possibly owe over $7000.00.  I was also told that they would be contacting my employer.  I told him that I wanted documentation before I paid anything and I was told they did not have to provide me this info until I had paid the money.  I was to go to Walmart and buy a prepaid debit card, fax a letter (and he told me exactly what I was to say in the fax), provide the prepaid debit card number and then call him back at 424-245-8902 that I had taken care of this problem.  I was contacted at my place of employment with regard to this matter.