These types of numbers which appear to come from inside Australia are in fact from overseas. I've been receiving them years, sometimes in the past more than 10 calls in a day.
Don't know what to do about them, being on the do not call register is ineffective. I used to have a very loud whistle, and when they answered I'd give them a blast. This worked for a while but not as well now.
My flip phone has a "White List" which blocks numbers that aren't on it, but that is sometimes inconvenient when you're waiting for a call from somebody not on the list. Perhaps we can send in Donald Trump to blow up these call centres!!