Caller: Scammers

This is a pay phone that accepts incoming calls in Guyra NSW, and I received 3 calls in the space of 9 minutes:
First call was a female, she said Hello and I said Hello back, then she said something incoherent after I asked "Who is this"
Second call was probable the same girl, she suggested I had $200 outstanding on my electricity bill, and I need to look at that. I replied "You have no idea what you are talking about, do you?" and she hung up.
Third call was a missed call but they left a message (which I will pass on to police if the calls continue), the caller was this time a male sounding screechy and irritated, he mentioned Tax File Number (not electricity like first caller) and $200 and a week, something about paying upright and he's sending to me in a week. Weird stuff. I'm intrigued, but will either pass on to police or the security detail at work.