Hi, welcome
I've had a lot of experience with the child support system as a non custodial parent with fortnightly visitation for my two girls. I paid all my child support plus many $$$ for extra care eg dental.
Bare in mind that the system does change over time and my experience dates back to the 1990's and 2000's.
Child support can accept evidence of income presented to them and in such cases they usually engage an independent solicitor to commence a review. That leads to a meeting between them and both of you whereby the care of the children is their number one priority.
The ATO downloads to the child support agency so when he does fill out a tax return his child support is calculated automatically and adjusted. He can adjust his income any time and adjust his CS, this was rarely done in the old days so that is an advancement.
If he is running a small business then that business declares personal income to himself, this means he has more regulation on his child support payments. If this is the case then income given to you from his ex could be highly inaccurate due to company costs, employees and so on so be aware of this as it could show him in a better light than he is in.
My advice is to always keep in contact with child support by writing, email etc as you have a printable account of correspondence. Write to them with your evidence (what you've heard etc as well) and ask for a review. I would not be concerning myself with whatever punishment the ATO could dish out, you are no longer together and child support is your sole focus now.
I hope this helps.
TonyWK
