Where do I even go from here?!

I originally received a letter telling me to confirm my employment income, so I went online and did this and my debt came out at a whopping $19,100.07!!
I called them and they informed me this was correct but they could run a reassessment and I'd have to go online and do the same process. So I gathered all my old pay summaries from employers to ensure I was entering the correct details, one pay summary actually varies from the amount they had shown so I corrected that and sent it off... weeks passed, I kept calling asking them why it hasn't been reassessed and if it has progressed yet, still no confirmed answer. In the meantime I received a bunch of amended pay summaries from centrelink, the amounts shown on the new pay summaries and the difference between what they say I was entitled to and the debt are two different amounts by around $4,000 (not including collection fees) so I called to tell them that they have clearly made some mistake because the notice I have says $19k but the new amount I've just added up in the amended pay summaries is only $14k... the lady on the phone kept telling me she didn't understand and that she would push my reassessment through.... two more weeks pass and I finally receive my reassessment... for the exact same amount from the first time! Where do I even go from here?!