Stressed and pregnant

I've had 4 different letters for 4 different amounts. Many hours in the phone, in person meetings, 'alleged' phone calls from appeals team...no never got them. All for an amount they have decided I owe from when I was actually a single parent with no financial support from the father. They have it all on file that I told them I was partnered and in full time employment but apparently they've overpaid me. No interest in all the day care statements that show the money stopped at the time I told them of this, no interest in looking at my bank acc statements that show I haven't received anything. Just the same response 'but the tax office says...'. Bub number two is due in two weeks. I've spent the best part of my third trimester of a high risk pregnancy stressed over this. I'm trying my best to get it sorted but they don't want to sort it. At this rate I'll be forfeiting my maternity pay to clear the debt. I just spent the last two years clearing all my debts so I could have a stress free maternity leave...fat chance of that! Thanks Centrelink!