Debt collectors are not selling you anything, therefore the FTC's Do Not Call program does not apply. The following URL links to the FTC FAQ page which the DNC site nearly begged everyone to read before you registered your numbers.

Q&A: The National Do Not Call Registry

Learn how to exercise your FDCPA rights as an alleged debtor at FTC-dot-gov. See also if your state laws are stronger.
 Jul 21st, 2012
Received call asking for another member of the household and requesting another number. Inquired as to callers name when advised commented we were on DO NOT CALL LIST and not to call again.
 Jul 21st, 2012
Called 3x today rings twice leaves no message
 Apr 17th, 2012
IC System. It's a collection agency. Lots of complaints against
this agency.
Ted Johnson
 Apr 28th, 2011