Be prepared for a long polite fight. You'll have to consistently insist on being accommodated in the same class of travel due to a Qantas ticketing error causing you Qatar flights to auto-cancel. As frustrating as it is, just don't be rude.
Same thing happened to me. QF Schedule change by 10 minutes, e-ticket not reissued fast enough, QR flights auto-cancelled. I only discovered same as you, by logging in. I was logging in every day to try find a better route home, so picked it up same-day.
Qantas requested QR reinstate. QR Refused.
20+ phone calls with consistent polite refusal to be put into economy class for our honeymoon. My argument was "My Qatar flights were auto-cancelled due to a Qantas ticketing error, I don't think it is reasonable for me to have to accept a downgrade due to an error on Qantas' end"
We were eventually put on QF9 on converted revenue seats. A garbage product compared to QSuites, but 1000% better than economy.
I was very lucky, this all happened when the "Priority" airport phone numbers actually routed to Hobart. I'm not sure how much harder it would have been if I only had contact with Fiji.
I would be e-mailing Tully immediately. 'Our flights on Qatar Airways were auto-cancelled due to a minor Qantas schedule change. The ticket was not re-issued by Qantas within the Ticketing Time Limit of Qatar Airways, this is the sole reason for the auto-cancellation.'
I would also be pointing out that you have had no communication, and theoretically could have arrived at the airport without a valid ticket due to no fault of your own.
Good Luck.