This guy keeps calling.  says he is calling for Mark

someone from this number phone my personal work number and left message.  The message was from someone (couldn't understand name) form IBM and to call back to 289-333-8372 - did not call back.

Calls for my boss, asks for him by name (the caller has a thick accent of some sort). I am my boss' call screener, so when I say, "may I take a message?", the caller responds, " I am calling for (some other name) and will call back when I can speak directly to (my boss)". I then say, "I answer the phone for my boss, so you will not get through to him. May I take a message?"  Caller says, "No, I will try to call back". I get this a lot, with different numbers, but the same spiel. Now, I just say, "Please do not call again unless you  are able to leave a detailed message with a phone number." Unfortunately, these calls come from different numbers, so I can block them, or report it... any advice?

Calls for me, gets my assistant, is very abrupt, hangs uop when my assistant will not pass the caller through.  Thick foreign accent.

They call several times a day asking for my boss. Never leaves a detailed message just always wants to call back.  Even when I say to transfer the call the person they are calling on behalf of is not available.  Totally frustrating.  If your boss is on another line why are you calling for mine???  I have better things to do with my time then answer the phone for people that have no real business to do!!