Had a similar problem with Optus when I moved. Kept getting bills even though I had rung them and notified them I wanted disconnection. Eventually I was advised that they I was continuing to be billed as I was being charged for the internet connection ? This occurred even though I had filled out the appropriate online forms .
They disconnected the phone but continued to charge me for the internet . They only fixed the issue when I refused to pay them any more money . It took 3 months . Good luck !
