Said it was Alyssa Smith from Telstra re my nbn. Gave this number. I doubt if its a legit call. No intention of calling back.

Caller: Kelvin from Telstra technical department

My internet connection is hacked, a number of foreign IP using, hence my internet usage will be high. He said he can assist me if I open the computer. I said I don't have a computer, then he asks are you using the smartphone and said he will check from their side.
I ask his number and the state he calling from. Without any hesitation, he provided (03) 9013 7013
Funny I am not the Telstra customer.