MR1100 DoubleNAT XBox One

I just traded in my old hotspot for a new Nighthawk, both from AT&T. Problem is my old one worked great for online gaming. This Nighthawk gives me the DoubleNAT and strict, and I can't online game. The hotspot is only connected to my Xbox and I turn the wifi off on my phone. Nothing else is connected. I'm not a tech type of person. So any help giving please break it down in simple terms or a step by step. Any help or advice will be great.