Dang. I kinda cannot believe how many people are dealing with this issue. I have the same thing here. I have an iPhone 7 and it has been working great.
I got a notice that I needed to update my iOS software or the carrier settings would stop working.
I upgraded, and to my surprise, NOW the carrier settings don't work. I visited the apple store, and was told I needed to buy a new phone. Seeing how long this has been going on, how many people are dealing with this, and the lack of an update, it seems a bit like planned obsolescence. Would love an update to be able to use my phone again.