We had a similar experience with QF95. We were booked in J with points, flight cancelled a few hours prior which added from 4 hour layover, a 17.5 hour layover, but we were rebooked with QF in Y. No care factor that we had organised this on the day the seats were released, it look like they were doing us a favour by giving us the difference back in points and cash.
I just raised a lengthy complain after calling customer service who were pretty decent to deal with, but just thinking, do you have travel insurance? In our case we ended up getting a day room as we arrived to LAX at 6 30am and we were leaving to Mexico until 11 30pm, which QF refused to pay for, but I'm aiming to get that through insurance.
Anyways, difficult position to be in, hopefully the trip wasn't that painful.