Much like the US, they can simultaneously have an economy that SHOULD collapse, but also be so ingrained in global trade that nobody is actually willing to call them to the carpet.

If China were Greece, they’d probably have gone bankrupt multiple times already.

If it’s still under warranty, they HAVE to unless they can prove your modification caused the system to fail. It’s no different than the silly stickers that say “warranty void if removed” - that’s a nice fantasy for the manufacturer, but at least in the US it’s been ruled those stickers mean absolutely nothing. If they’re refusing to fix a phone under warranty, contact your local AG and enjoy watching them squirm. Loop in the FTC for good measure.

https://www.ftc.gov/business-guidance/resources/businesspersons-guide-federal-warranty-law#Magnuson-Moss