My advice to you is this:
Never give up
I've been fighting child support for the past 7 years as XH gets a job, looses a job & has long periods of unemployment.
I work "school hours" & pay for "everything" for my 2 girls.
The child support system sucks so badly in my country that just this week after going through my 6th child support hearing because I had been set to zero (the 2nd time this has happened) I was left with a $1700 bill at the end of it.
I hadn't received much & what little I did turned into overpayments because they re-estimated his annual income & backdated it to April 2013.
So not only am I struggling to pay for everything but not I am in debt.
Each time you go the situation again you learn a little more.
I thought I knew most of it until this last lot.
Honestly sometimes I just want to bang my head against a brick wall.
Each time I fight it is an incredible time consuming jobs to fill in forms & produce financials.
But I have done it & I haven't given up.
Another piece of advice - keep everything, receipts, bills, income proof, drs visits, the lot. The more you can prove the better result.
Good luck.
I know just how you're feeling.