NETPROCO is the one calling. They use this number 720-729-1793 and also 720-398-0170. http://netproco.com/index.php

They call using a fax sound. The Better Business Bureau has several complaints with this number 720-398-0170. http://www.bbb.org/denver/business-reviews/te ... 0852/complaints
The BBB has this on their site "BBB was unable to locate business to process complaint (33 complaints)"