How do I fix cellular update fail

Well, I had an appointment at the Genius Bar, so I drove an hour and a half just to be told by Apple after they ran some checks and reset on my phone, that it was not a software problem it is a hardware problem and they can’t/won’t fix it. This is not true Apple. My 6S was brand new four months ago , out of the box, and I had no problems with it until I updated to 12.0. The manager, if she was actually the manager, even told me she had never seen that message before. I said, “really? Because if you go on Apple support under community discussion there are quite a few people that this is happening to. “. She replied with “ no, we don’t read those because you can basically hear anything you want to hear“. APPLE THIS IS WRONG WRONG WRONG! I have to buy a new phone all because my phone software loaded 12.0 while I slept and it’s a HARDWARE problem???? This is UNETHICAL APPLE!!!!!