This number calls me "out of office hours", requesting to be called "in office hours, they give you a reference number and say they are USB?

They are the United Collections Bureau (UCB).  The number they want you to call is 866-559-4304, but the number on my caller ID was simply "419."

After researching this number, I found they have a BBB rating of "F"- which is the worst you can get.  It has been reported many times as a scam, and they have also been reported for multiple collection practice violations.

I get voicemails at work several times per day from "Mr. Miller" providing this telephone number and a reference number.  States I "MUST call him back IMMEDIATELY."  When you call the number there is no formal greeting advising what company you are even calling just to either enter an extension number or hold on the line for further assistance, something I simply will NOT do when I have never done business with this company before or any company that would use scum-bags like this to collect on their old debts.  From what I've researched, they purchase tons of junk-debt that is no longer collectible and also try to scare people into paying for debts they no longer have balances on.  Sorry "Mr. Miller" no matter how many times you leave your crazy messages on my voicemail, I will NOT be calling you back.  My Cease and Desist letter to you will go in the mail this morning.