He's not telling you to get lost he's telling you to come directly to where the buck stops, with him. Apparently you were told the same thing by the bloke in the same position previously. Your letter gets very personal with statements such as:
Then I plan to spend the time I have available in communicating to everyone how dishonest your organisation is and how it is amazing to me that you can sleep at night.
From what I can tell about Mr Skidmore's reply:
I found the language and tone of your letter unacceptable. Gerard Campbell is a highly qualified, highly experienced and highly principled member of my senior executive team. Neither he, nor any other CASA manager or staff member, should be written to in this manner.
he is defending his staff which was one of the attributes we expect from a good leader.
With your public profile I am surprised that you would not have just spoken to Mr Skidmore directly instead of publishing private correspondence between you and CASA.