Where to go if CASA do not rule in your favour, I'm not so sure.
However, if you feel you have been treated unfairly, or CASA haven't justified themselves in your ruling, The Indutry Complaints Commissioner is a good place to air your concerns.
Unfortunately, I've had to raise my case with them once before, within 2 days of the complaint, my problem was rectified. So definitely worth a go.
About CASA - CASA Industry Complaints Commissioner