I love bill collectors and stating "He doesn't live here anymore" hehe...

Umm they can't get you for calling back the number as you're just trying to be removed from their list.

You may want to try a reverse search on the number at like http://www.whitepages.com and see if there is any info on the line; a lot of the time you'll find company or individual names then be able to check for any additional numbers.