Okay, you should be able to write after a week. There’s an important difference between the xDF2 and the NExT that is preventing you from using it out of the box.
The NExT has all of its memory formatted as NDEF by default, which is what phones read when they open websites and such from a tag. The xDF2 is a more advanced chip that has a file structure and can be used for lots more stuff. You can just format it as a big NDEF container, which is what most people do. You just have to use specific apps to do the initial setup.
The one I recommend is provided by the manufacturer: TagWriter by NXP
Unfortunately I only have an Android, so I’ll share screenshots on that version of the app and you can figure it out on yours.
