That's what i did. Get the # off caller Id and call the phone company to see who it belongs to. Then call the head of the company.
I got the phone number to return the call but it's constantly busy of course. I did call similar numbers - the first five digits and then added two zeros - and finally got a company that said it "might" be one of their numbers. In the meantime I'm trying to find out how to 'call forward' to a friend's answering machine.