bzzt try again
The TIO is not for this kind of thing. The TIO is to settle disputes between you and a Telecommunications Provider (Phone or Internet).
If you don't read the fine print in a contract and are obliged under that contract to pay for data usage, it's your problem, not the carriers.
Whilst Telstra may be a rip off, they're 100% allowed to demand payment and not write it off or have the TIO tell them to do so.
The TIO is the most toothless tiger i've seen. They don't care about anything but revenue. Opening a case with the TIO immediately passes costs to the providers. Passing costs = increase in telcos costs.
If you can't read the fine print, you shouldn't be using the service. Jumping up and down like a petulant child does not do anyone any favours.