First off, they hadn't sent me a bill for July, and secondly I'd already taken the precautionary step of paying enough to cover the likely charges.
I phoned and was given the usual runaround on their useless call line. You would expect a phone company to manage that side of things better, but no, they dropped the call twice, then announced that I should go online and read the FAQs, and then, after half an hour of this, I finally reached a human: a woman with a strong Asian accent, who spoke swiftly and sotto voce. My hearing is below par and so the conversation consisted of me asking her to speak more slowly and to raise her voice, while she continued as before.
When she finally comprehended that I had a question about my non-existent bill, she thought I was asking for the balance, and suggested I use their app (which I discovered later was for iPhones only, while I'm an Android user).
I explained again what the problem was, and she said a bill had been sent. I disputed this, and she disappeared for a couple of minutes before returning to say there had been a software glitch and they were looking into it.
She then tried to persuade me to add my Optus mobile phone to my "bundle". When she realised that I wasn't go to yield, she said I should have a website and they had skilled developers who would build one for me.
I told her I had multiple websites and built them myself. She thought I was a very smart person for being able to do that, abandoned the sales spiel, and hoped I had a nice day.