First thing to do is change any passwords you have anywhere online, obviously concentrate with any that deal with financial matters and transactions - THIS SHOULD BE DONE FROM ANOTHER SECURE SYSTEM also once you have done this disconnect from the internet, and run a full scan for the main types of malware, Adware, viruses and it is a good idea to do a boot scan for keyloggers and the like.
Your computer could have been compromised at a low level and may be sending all your important information to someone who will not use it for your benefit
This is of course only a possible result of the attempted "Telstra" scam and I hope this is the case but better safe than sorry
If you have backups of images before the incident then these should be clean if they were not left connected to the system and can be used to restore the system. I would suggest that you do a full fresh reinstall, if you need to get backups of your data then do not return them to the new setups until they have been fully scanned