I used to have 50 50 (week on, week off) custody of children for my daughter until 3 years ago when she was diagnosed with diabetes. She wanted more time with her mum and I agreed as it was what my daughter wanted. My ex notified Centrelink about this but not Child Support Agency. I figured she didn't make the change so as to prove to me she wasn't doing it for money. But apparently she never read her Child Support Agency statements and didn't know that it wasn't changed from 50 50 to the new arrangement (3 or 4 nights per fortnight). Now she's saying she can lodge a claim and make me back pay the difference. Is this true?