I'm so sorry for You but even if Knox was tripped You can ask for a repair in warranty if You live in Europe. I'm a consumer lawyer and for my clients I always get warranty service from Samsung even if they try to refuse the reparations.
Well I would have done that, I live in Germany but it would have taken them quite a bit of time. I sold it for 500 euros and explained the issue to the buyer. I bought a nexus 5 and Nexus 7 2013 with that money. To my surprise the Nexus series do NOT accept USB OTG natively. I had to get Stickmount from Chainfire to use any additional storage. It really made me wish for my note 3 back even with the sensor issue.
When my wife got the s5, I immediately realized why I like Touchwhiz and its lag. It comes out of the box with a lot of features that other devices need root for..
Like USB OTG
Customized quick settings
All share, (no need for all cast)
Also its cameras are always better with its features.
Plus micro sd
Battery removal and last but not least, It comes with in my opinion the best screens. I love Super OMLED.