afni sending letter for Sprint bill from I don't know where

I received a letter from afni saying I owed 51.97 from Sprint. I called afni to let them know that I am now and have been a current customer of Sprint over 10 years for my cell, and have no outstanding bill due. Sprint just does not let you pay...anyone who uses this company knows this.

Of course the young man insisted that this was a bill from a long time ago. I informed him that I had just recently checked all three credit agencies to check my scores and they show nothing for this bill. He said it was too old to show. Well if it was that old I was not with Sprint then.

I said this call was to inform anfi they have the wrong person, he said "no"... I just said "have a nice day". click.

Now I have received another letter today saying they have re-checked with Sprint and this is in fact due with I feel bogus creditor account information.

All this time and Sprint has never sent me a bill for this...come on....

So now after reading this site and others I will write back asking for a copy of this so called bill, not just their word for it.