I received an email from Jetstar today notifying me that my flight from Hobart to Cairns transiting via Brisbane has been cancelled. They're unable to move me to a new flight and will be reimbursing me with a Jetstar travel credit for the same amount, valid for 12 months. I won't receive this credit for at least two weeks. I just checked their website and my flights are all still available, but are now $600+, three times what I originally paid for the same route.

This is the exact wording: We’re sorry to let you know that your flight/s on booking XXXXXX have been cancelled and we are unable to accommodate you on an alternative service.

It's obviously incredibly unethical but is this kind of thing actually legal? I purchased a service from them for an agreed-upon price, and now (I imagine due to demand) they've broken that contract in the aim of getting more money. The flights are still happening, I just can't afford them now, particularly now I have to wait at least two weeks to get this 'travel credit' (and not even my money back to buy a flight with Qantas, which is bullshit).

Is this legal? What can I do? I haven't seen my family in almost a year and I'm getting desperate to go home.