Caller ID said 'NOT IN USE'. I almost laughed. Someone chose that one. So, since it is not in use, I picked up, but said nothing, and was responded to in the same way. After about 20 seconds I just hung up.
you need to understand HOW the Do Not Call registry works. It works for legitimate companies, not illegitimate ones and certainly not ones that manage to have a loophole to allow for telemarketing calls. And to report a harassing phone call you must speak with the company and verbally request they stop contacting you. You can't just go about saying "This number called me and left no message" because they don't consider that harassment.