In the good old days of HF communication using the morse code, the sending of:
_._. _._. = C C = Charlie Charlie
Was a quick way of saying Affirmative or I have received and understood your message. When HF morse gave way to HF voice, the phrase "Charlie Charlie" continued to be used all over the world. I am retired now but I am sure that "Charlie Charlie" continues to be used in many places to this day.