At that point, is there really anything that we can say or do to help?
Your best bet is to go to the Apple store and try to get it swapped, hopefully under warranty at the very least.
My friend had a 7+ that would refuse to pick up anything from the SIM, like it would be fine one second and any point afterward it just simply died.
The people at Apple ran a battery of tests, including running a new SIM and they gave him a brand new phone as compensation.
Maybe they can arrange for something like that for you, just make something up like: "I've tried resetting it 4 times, I need my phone for work and this is really frustrating..."