They keep on calling 2-3 times/day! No message left. My number is registered to FCC DNC numbers. Why are they allowed to bother people during the day and night???
After being called continuously I finally called them and got a customer service number to call. I called and had them remove our number from the list. They were very pleasant to deal with. The customer service number is 866-544-4880.
Calls of uncertain origin for which you cannot really pin down the source may be (1) collection agencies to see if you ever answer the phone, OR (2) VoIP numbers (Voice over Internet Providers). In the latter case, someone may simply be checking on you/stalking you -- a potential or ex- lover, etc. VoIP allows someone to call you through their internet phone (many people pay-per-call to use the same number). If you call back, you reveal your own number (even if you attempt to block it). Your pesky caller is then routed the info that you called to check on their call. In cases of unidentified callers, check this site and others like it, and check the number universally on the www. If you find a great variety of people getting strange calls that never seem to be traceable, it may be someone you know (or who knows you) calling via VoIP.