I didn't answer, left no message.

Caller claimed to represent a veterans' charity.  My wife answered the phone and said she couldn't talk because she had to leave for an appointment.  The caller rudely said, "Why did you answer the phone, then?"  I tried to call the number back to demand they stop calling us, using caller ID to call the number, and got a message: "invalid number; please check the number and call again."  Checked the number, called again, same result.