Random Calls

I just got a call from Nathalie at Telstra. She was very helpful, although I still have no internet and no ETA on it, she seemed to be doing what she could. My question is, is it REALLY the law that if a company calls and asks to speak to me about my bill, instead of there being a system of mutual trust, I am expected to provide my personal details to some random person on the phone, who may or may not be who they say they are ? I can see how that protects Telstra, but I do not see how it protects me, if someone calls on the basis of pretending to be from Telstra, so they can get my personal details.

Add that to my broken internet, and I confess to starting the call badly, unlike prior callers who I have refused to give my details to, she refused to tell me how many accounts I have, etc, but we got through it with the reference number from the Ombudsman. The reason there is so much internet fraud is that people just comply with these sort of requests, and every once in a while, be it an email or a phone call, something comes in that is not what it claims to be.