RJM Acquisitions LLC Purchased Scholastic account, closed due to inaccuracy, and reactivated 5 yrs later trying to collect again Syosset, New York

Received notification in 2010 for a Scholastic account debt from RJM Acquisitions, dating back to 2008 signup of Babies First Disney Books Book Club. 

Called and resolved with RJM by closing the account because the debt was inaccurate.  Jump to February 26, 2013, received same notification for debt of $37.90, presented with several methods of payment to debt collector RJM Acquistions, also including "This communication is from a debt collector, is an attempt to collect a debt, and any information obtained will be used for that purpose.  See back of letter for important information."
Formal instructions on back say "Unless you notify this office within 30 days after receiving this notice that you dispute the validity of this debt or any portion thereof, this office will assume this debt is valid...."
So it looks valid, but couldn't get over knowing I had resolved this in 2010.  After calling them and simply stating "I resolved this in 2010" - nothing else, no documentation, no proof - they said "OK, I'll take care of this.  Thanks."  Scammers.  But they certainly would have accepted our payment!  Probably within the law too.