Didn't receive a letter lucky my mum did though!!!!

Centrelink said that they had sent me a previous letter to which I did not respond to, I did not receive the first letter as my mother is my second contact person and she received duplicates of all my centrelink correspondence and she did not receive the first notification . This matter only came to my attention when my mother received a letter that Centrelink were taking action with threats of debt collectors and recovery fees because of an alleged over payment.

I searched bank statements from banks as I have not been employed casually or part time by Coles for 2 years.
I don’t consider I did anything wrong or illegal and I had to show my payslips to centrelink during that period I was receiving a newstart allowance as well as a complete tax return. I had to move to another town to get work as there was nothing around home area.

I contacted centrelink office twice, regarding this matter, they were to get back to me and I still have not heard from anyone.
I feel I have not done anything wrong, or illegal but have now been put in a position to where I now have to justify some type of wrong doing or illegal activity which is completely out of character for me.

I contacted centrelink then as no one had contacted it was being reviewed as I did have a knee injury during that time and did not work for a few months after that review it was still the same about so I appealed hadn't heard them for a week or 2 so I called them was put through to someone else and she tells me that I need to get payslips when I appealed for the first time no one told me this information it is like someone tells you something differently all them time.

But I do not financially have the money to pay this as I am living out of home renting bills etc.