Thanks for taking the time.
I have seen both of those posts, and even though neither address my problem exactly (I get a blank screen with the text that says that “APN settings are not available for this user”) I have already tried those suggestions. None of them work. There is no “configure card”-line in my SIM Toolkit. And nothing changed after undertaking the shutdown routine.
As I wrote in the first post, I can seemingly add a new APN (the +sign is still there) but upon saving it, nothing happens. The same message (“APN settings are not…”) is still there.
This is how it looks:
