I accidentally booked the wrong day on one of our flights. As it was a cheap fare we couldn't change the flight without the $60 fee, and as there was two tickets that was a total of $110 suppository fees, more than half what the fares cost. In the text chat I was also told that canceling my flights would forfeit my entire fare as the fares I chose were apparently not refundable.
I was outraged and complained at length on the text chat. Finally I called the 13 number and was told the same thing.
They offered me a $50 voucher as a gesture of good will, but it it was not for each ticket... just a one-off, and would also mean I had to fly Jetstar again.
At that point I requested they cancel *ALL* my flights, and explained that regardless of whatever terms and conditions I had clicked agree on, I expected that I was well within some kind of "grace period" on ANY purchase made mere minutes ago.
They put me on hold again to check on cancelling my flights. After a few minutes they came back to tell me that through some miracle they were suddenly able to waive the fee on changing the flights. I paid the small difference in fares.
This is the story of how Jetstar wiped themselves off my list of viable airlines, but hopefully will give you ammunition to save yourself some money.