I went to Cuba in 2016 and all I worried about was having enough money. So much so, I found an ATM in Havana that would dispense cash on one of my cards and noted the location. I figured worst case scenario a taxi would take me there and I could get cash. I also made sure I hade euros left over as I could easily change them back at home or use them on my next trip.
Of course rechecking flights is also something I do and you should be able to see all the one world bookings when you log onto your frequent flyer account.
Anyway I'd argue that Qantas probably stuffed up to some degree, but it was avoidable also. That said I'm very well travelled and I always take precautions, even as I write this from Riga in Latvia, a fairly easy place to get around, I have about 100 Euros in cash I'm trying to not use, just in case. However, I've met other intrepid travellers who feel everything will work out eventually and ing it far too much for my liking! I'm sure you were, however, thinking everything was fine and planned.
I was detained in China once and I know you don't think straight and just take whatever option it is to get out of there, but you probably could have flown to Panama city cheaper and then looked at onward flights to Madrid perhaps.
I'm not sure you'll get much out of Qantas, because it should have been clear to you there was no ticket issued. Anyway, I hope over time you'll look back at the whole situation as an experience and maybe even laugh about it. I know I do with some of my more horrific experiences over the years. Now I better get going I'm off to the bus station to go to Tallinn and worried my online ticket purchase may have issues as I can't print it out!