Caller: NBN co.

I recieved three phone calls today one from this number with a recorded message stating they were calling from the NBN with a threat to press one and speak with a technician or else landline and internet would be cut off. I don't have a land line.

Sounds very similar to the one I received from (02) 4257 1036. How are they able to clone so many phone numbers? I get up 10 calls a day from these clowns, 6 am and 12am and 3pm no rhyme nor reason, sick of it. I rely on my phone for work and don't want to have keep changing my number. It's RIDICULOUS!