What do you mean by Scam Billing? What type of charges have you incurred?
Best bet would be to discuss with the Billing & Accounts Team via Live Chat at http://yesopt.us/chat2us and discuss/dispute the charges. If you are unhappy with the resolution, you can always lodge a complaint to have it case managed. Most plans now days have unlimited calls and SMS, are these international calls and SMS?
Opus is fuelling scams by selling scammers local phone numbers. Each time legitimate customers are "nuisance called" or sent scam texts they are billed at a premium call rate. The fix is very simple and there are numerous ways to apply them if Optus is genuinely interested in forgoing the extra income. I suspect that the issue is all about the money at the expense of legitimate customers enjoyment. If you urinate in an open fire for long enough everyone will vacate sooner or later.
My own experiences include being charged for 3rd party scams. My plan was a $50 plan discounted to $45/month. Most of the plan is data usage and a few legitimate calls and texts so the bill should be $45/month as my budget is very tight. The billing service firstly ignored the discount which took 2 months to fix and adjust and ignored billing me for 3rd party scams. This is a tech problem and if the tech people who created the billing service cannot fix a problem they created, repeat billing me and other customers wrong with Optus management. Secondly, it's illegal to sell known repeat scammers a service that stuffs up a legal service. There are 2 parties at fault here. Optus senior management and the government regulators who have a number of ways to enforce their own rules and regulations. 3rdly the bills do not show the running account at the top of the account so the customers can see problems will billing straight away. Currently, the final figure can only be seen at the bottom of a long long long page of data. That effectively cuts out mobile users.