This was obviously a potentially dangerous phone call. A recording said that my Optus account would be cut off unless I pressed one of the buttons (I cannot remember which one) on my phone. This was obviously a fake since I haven't had an Optus account for about 4 years, and was also subject to the Optus data breach (that was also well after I had an Optus account). Obviously someone who stole my data was making use of it. Easy to detect i this case. I blocked the number, but it is probably fake or a "throwaway" phone.
But this is a very good example of what to avoid. As numerous agencies say, if there is a (fake) sense of urgency, it is almost certainly a fraud attempt. I simply hung up and reported the number to the ACMA. Beware!