I called back number 0488 824 511 reached IVR for the Acm Group Limited.

keep calling me in regards to a payment I have made. have sent reciept but they say they haven't received it yet. nothing bounced back into my account.

Harassed me for a decade,calling relentlessly under multiple numbers-up to twice a day in the early years-claimed Court decision against me that never happened-bombarded me with fake notices and then tripled the claimed debt.
Rejected an early offer of $100 week if they could prove there was any legitimacy to their claim,demanding I borrow the entire claimed amount from a friend, family or Lending Agency-constantly threatened action within 24,48&72 hours which never happened,causing untold stress to my family and I,until I came to the view that they were phoney.
Asked them early on to correspond by email only, where they couldn't change their story whenever it suited-something they refused to do.
Not sure what constitutes illegal behaviour in Australia, but surely a decade of this is not lawful.

ACM Debt collectors - a-holes