Also lodged an online complaint about billing to telstra, then received a phone call from this number that hung up immediately before I could even answer. Is telstra really this dodgy or is someone else hacking them?

These guys phoned me twice, claiming I owed Telstra over $400 and that they are collecting the money on Telstra's behalf. I followed this up with Telstra and they confirmed that I did not owe them anything. This is definitely a hoax or scheme to steel money off unsuspecting victims.

Overseas accent, garbled message, I rang back and they put me on hold and the call ended.

Couple of calls to the home number and asked for various names of account holder none of which was correct & then a call to my mobile - they didn't leave a message. Had a thick accent

rang them back after missing a call ,sounded like voip so i asked where he was ,philipines so i hung up