I received a call from a ?telstra tech who said people were using my telstra internet. He sounded reasonable but telstra did not have my new Optus phone number. He wanted to put me through to the tech dept to fix this. I told him i did not know if he really was telstra and i would phone the tech myself which i did. They confirmed they had no record of a call. It was a scam and they had received a lot of reports.
We do have a support page that offers a number handy hints.
I always suggest registering your details with DNR.