I'm not sure from your question if you are unhappy with the CSA determination of level of child support that should be paid, or if you are happy with the CSA determination - but the payments have not been made at the determined level.
It sounds like he has organised his affairs to have a low reportable income to the ATO. But that is not the end of it. See this page ;
http://guide.csa.gov.au/part_2/2_6_14.php in particular Special Circumstances and below. You will see that it it possible to look behind the family Trust and corporate structures in certain circumstances.
If you are unhappy with CSA's determination you can apply to the Family Court ; See http://guide.csa.gov.au/part_4/4_3_2.php
You would make a s116 application ; See http://guide.csa.gov.au/part_4/4_3_2.php#s116
Then go back and read this ; http://guide.csa.gov.au/part_2/2_6_14.php#alienation_of_income_corporate_veil this sounds like the situation at play here.
Ultimately, you need an enforceable court order. Non compliance with court orders simply isn't possible.
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