[BenMcr]

It says it on the FAQs if you read them

Is there a minimum contract period?
Yes, a minimum contract period of 12 months applies to National Broadband services.
However, if you cancel the service during the 'cooling off period' (seven working days of entering into a contract) no charges apply

and

You also can cancel the agreement without penalty up to the date of your Talk activation, however we would request you inform us as soon as possible, preferably prior to your broadband activation date

and

Cancellations
If you want to cancel your National Broadband service before your line is activated, you must notify us by phone. You will need to call the Cancellation Line. You can find details on our contact us form.
There are no charges for cancelling prior to your Broadband activation date


Basically you can't cancel once you line is activated without paying out the contract