Calls and doesn't leave message, cannot find owner info and not a contact in my phone so no answer.

Calls my work number multiple times per day. Can only hear background noise. If I answer, they hang up. If I let it go to voicemail, they have been known to let the call go well over a minute and a half and never say a word. Called back, and the message says to 'press 1 to speak to an agent, 2 to permanently remove your number from their call list'. Neither option works. More dead air. Their ID comes up as NONE. I have no idea who they are.