Debts raised for 22-23 & 23-24 financial years after my payments were balanced.

So I revived two letters from Centrelink saying I had a debt for almost $2000. After finally getting through on the phone, they’ve advised me it’s because of a change in my ex partners income (child support payments) That’s totally fine and I’m happy to pay back what I wasn’t entitled to, obviously. I’m just not happy with the fact they balanced my payments, PAID ME an extra amount of money & now, years later they’ve decided I owe them money. This could honestly put some people in a bad financial position especially in this climate. Just think it’s a flawed system to be honest. Anyway, thanks for listening to my rant 😆