Trying to do the right thing...

I am a single parent, have been working part-time and periodically since my son was 7 months old, and full-time for 15 years prior to having him. I have been contributing taxes for 22 consecutive years. I put myself through uni part-time whilst working full-time without any government assistance whatsoever, not even a free bus pass... I am a teacher, therefore I work during school terms. In 2013/14, I did a combination of full-time short-term contract work (max 2 terms) and relief teaching, therefore don't get paid in the school holidays. I earned a reasonable amount of money, still less than my full-time wage before having my son, but enough to contribute almost $13k in income tax that year. This amount also included a $7k back-payment for work completed in the previous financial year, but due to the stuff-up of the government department I was working for, I didn't get paid OR any Centrelink payments for 7 weeks, and it was finally finalised and put in my bank on the 4/7 of the next financial year, bumping my annual earnings by approximately $7k which should've been paid in the previous financial year.

I received a letter just after Christmas saying I owed almost $5k in overpayments, as they averaged my income over the financial year, rather than the fortnightly earnings I was reporting at the time. Given a lot of the work I obtained that financial year was full-time, I was getting NO pension, and given my son was only 4 years old at the time, I could've been sitting at home, collecting a full pension and contributing zero tax if I wanted to. I was entitled to do that, even though I thought going out to work and relying on my parents to help take my child to kindy and grapple with the guilt that working mothers do... But no, I WANTED to work and be financially independent when the workflow allowed me to, therefore only receiving a pension during school holidays or short periods of time where workflow was low (start of a new school year is notoriously slow for Relief Teaching). Given I saved the Government THOUSANDS of dollars in a pension I did NOT receive during school term time due to my earnings being above the threshold, and the $13k income tax I paid that financial year, I am astounded that I have now, 4 years later, been slugged with an almost $5k debt, when I could've been sitting on my arse collecting a full pension and contributing NOTHING, and there would be no questions asked... An absolute disgrace. I am fighting this with everything I have and will go right to the top if I have to. I am currently waiting for them to assess my case after providing them with the evidence of periods where I received NO income...