Justin White Cash Advance USA Harassing phone calls to my place of employment, conned me out of money I thought I owed Nationwide

Four weeks ago this Justin White person started calling my place of employment and my cell phone claiming that I owe for a defaulted loan from 2013.  I tried to ignore the calls but the calls to work were so frequent and harassing I had to call him to try and get him to stop calling work.  After a conversation, he had some information that led me to believe I may actually owe for an account that was closed on a bank account I closed 4 years ago.  I should have called the FTC immediately to file a complaint but instead I actually paid the idiot in a way that could not be tracked or traced (completely stupid error on my part).  He called me back to say I know owe for the "2nd allegation" and the amounts get larger with each "allegation".  I've asked for all of the pertinent information a debt collector should give you when trying to collect a debt but he would not cooperate and told me I just needed to pay!  After completely ignoring him for days the calls to my work have started back up with a vengeance.  It's so out of control we have to have someone man our switchboard.  We are trying to block their telephone numbers but let's face it.  They aren't calling within the US.  I'm filing a police report with our sheriff's department to try and cover all of my basis and I've filled a report with the FTC but it's really not stopping the calls to my work.  He even said he would "continue to call my work and harass them until I paid".  If I can help anyone with my mistakes then this is work the time to write!  The numbers he's calling from are 917-477-8945 and 912-235-0808.