Got same message three times and it was threatening that if I don't call back, a seriously bad situation is about to unfold. Listened to the message several times as the voice was not so clear, but any "Officer" whether from provincial or federal government will not leave such a message. They are always respectful. If these calls are valid, and indeed from a CRA officer, they normally send mail or e-mail so they will be contacted properly.
Got the same message once. He said he is the Officer John Parker and if I don't return his call I gonna have many problems. Someone know what the Hell is that ??