many calls, no message left. ANNOYING!!!

First time for this number. However, called at 7pm.  These daily calls from "unknown caller" are getting annoying.  Not to mention area codes from Cambodia, Jamaica, unassigned area code  AND the "spoofed" numbers.!!!  The Do Not Call list is worthless.  My question is:  WHY do these people do these harassing calls?  Is our next generation only interested in how many people they can Annoy ?????