Just had the exact call but referring to NBN (it was Nicole) - but she called from (02) 9563 6825 - she gets about.

An automated message starting with "Hi, I'm Nicole from Telstra..." saying that my phone and internet will be disconnected within 24hrs.. press 1 to talk to a technician. I hung up of course. Telstra does not make these kind of calls. I know I'm up to date with my bills and if I wasn't I'd still hang up and call the 1300 to talk to telstra myself.