Invest in a call blocker.  Callers are most likely hard core Indian or Pakistani scammer extortionists.  THey often engage in sexually aggressive talk when they find their scams are not working.

Called just now. Hit the ol decline button and then the block caller button. Not that it matters much, they'll just spoof another number.

robocall on my phone from   217-468-7643 caller ID said "UNKNOWN NAME" on Friday 01-20-17 at 1259 PM.

Unknown SCAM.
wanted to try the suggestion from another poster from a different call.
phone rang . I answered it - "Hello_Hello_Hello_Hello_Hello"  (multiple more times etc) in rapid succession).
It did seem to help disconnect the call as the other poster suggested - making the robocall think you are an answer machine.
will need to try a few more times to make sure it was not just a fluke occurrence.

Some one call from this number but didn't leave a message. And I don't know the number so I didn't answer.

robocall on my phone from   217-468-7643 caller ID said "UNKNOWN NAME" on Monday 01-23-17 at 230 PM.

guess SCAMMER calling since they did not talk to me last Friday.
card member services with strong india/hindi accent asked me "how are you doing today?"
told the SCAMMER "was doing OK until a mxxxxxxxd (expletive) SCAMMER came on the line. How is Mumbai treating you
today mxxxxxxxd (expletive)." SCAMMER said nothing then hung-up.