After spending many hours on the phone trying to get answers and a clear explanation of how I incurred my debt, I finally gave up and accepted the debt.
If I wasn't busy with work and family commitments I would have fought it more.
After I began the repayment process, I received a letter from Centrelink advising that I need to make an amendment to my tax returns in the years in which my debt was accumulated. This is because as I am now re-paying my debt, my assessable income for those years has now been reduced meaning that I paid more tax in those years than what I needed to.
The only problem is the tax office is saying that I cannot make an amendment to those tax returns as the time period lapsed is too great.
I have attempted to contact Centrelink to explain that I should have the additional tax I paid taken off my debt, but they are giving me the run around saying to take it up with the tax department.