Caller ID reads "7543070402" instead of the standard form (754) 307 0402, so the caller ID is spoofed to look vanilla. They leave no message.
I call after hours (using *67 to block my number). I hear "No routes found. We're sorry your call can not be completed at this time. Please, hang up and try your call again later. Thank You" Then it hangs up.
So they spoof their caller ID and don't seem to be able to be called back. Smells like a SCAM.