This number called the office this morning twice within an hour.

Call #1:
Caller: (Robocaller) "Hi, this is Kate from Google Plus..."
Me: *click*

I let the second call ring unanswered, and "Kate" chose not to leave a message on our answering machine.

Although there are probably scores of these numbers, here are the ones where I've confirmed in my log that robocaller Kate was on the other end:
http://800notes.com/Phone.aspx/1-248-289-9121
http://800notes.com/Phone.aspx/1-248-308-1208
http://800notes.com/Phone.aspx/1-714-784-5853