Caller: "Nicole" from the "Australian NBN"

I have had this exact phone call many time and is probably a scam. I do not answer the phone, but the voice message I received (automated, not a real person) said this: "Hi this is Nicole from the Australian National Broadband Network. We have been trying to get in touch with you. However we are going to disconnect your land line and Internet connection within 24 hours as the NBN services are now available in your locality. So I'm interrupted services. Please press one to get yourself connected to the technician."

The whole thing doesn't make sense, why would they say they are going to interrupt my service if NBN is in my area? And I have already been on the NBN for 18 months now.