You could always pick up the phone and ask who it is! Cray cray idea I know.

How can you find out who is ringing, if no results are found on your website?

It may be a telemarketer, they call often but are either disconnected or no one speaks when I have answered, no message left if I miss the call.

Telemarketers. This number calls me every business day and doesn't leave a voicemail. I called back and received an automated message saying that they were calling on behalf of one of Australia's charities.