Very slick legal judo: You were "invited to comment" or "invited to respond" three times in that letter to what are simple assertions by CASA. If you were foolish enough to take the bait, then you are implicitly accepting the truth of CASAs assertions as fact. It's called self incrimination.
This is in effect a series of three "when did you stop beating your wife" type of attack. There was no "show cause" notice because that would have raised the self incrimination alarm because we all know how to answer a "show cause" letter.
Grrrrr.