Perhaps try going in, if possible, and see what they can do?
Why did it cost $500 for a screen protector, or was there screen damage as well?
You can tell them it was replaced before and failed again and see what they advise.
Depending on the outcome, you could try looking for a Korean phone shop that sells the Whitestone Dome Fold and Flip protection film. I'm not sure about other companies that produce them.
Edit: you won't get much if you sell it as it is, but you could ask the store about trade-up 🤷
Do not remove screen protectors from flip phones, it clearly states it will void any warranty and therefore your recourse in escalating the complaint will diminish.
For more information on how to back up your device: https://www.samsung.com/au/support/mobile-devices/back-up-samsung-device/
To book an appointment prior to heading in-store or to drop off your device via Australia Post: https://www.samsung.com/au/support/your-service/main
To find your nearest store: https://www.samsung.com/au/samsungstore/
Exactly what happened to mine. Eventually, the bubble gets bigger until finally one day you close the phone shut and you will hear a popping sound, this then leads to a screen bleed.
The first time it happened Samsung replaced screen under warranty. 2 months later the bubbling/crease line was appearing again, until August i heard that dreaded popping sound, screen bleed again.
This time I no longer wanted a replacement, to me it's a lemon. Samsung now say physical damage to the phone and not covered. Nonsense!. I'm taking it up with ACCC. Had the phone for 18months and this keeps happening, a lemon batch is all I can say.