I never get these calls. I'm not sure if it's because I don't have a landline?
I did have an unexpected call from centerlink a couple of weeks ago. The guy sounded most confused when he told me I had to answer some security questions, and I said 'how about you answer some from me? You've called me on a withheld number. You could be anyone'. 'I can't talk to you if you don't answer the security questions'. Ohhhh no lol. I've had Vodafone do the same.