Got a call from this number and no message left.

Call to my office...I didn't answer...no message left. No Caller ID shown.

Called regarding a virtual assistant.  Said "not interested" and they hung up.

Took a second or two for them to reply to my greeting though.  Probably not used to getting answers.

Called my office asked for my boss - i asked "who's calling and what is it regarding?" they hung up immediately

Call and asked for me.  Told them I was speaking and they hung up.