Nighthawk M1 speed

I am new to the community and new to the whole hotspot router. I bought a nighthawk M1 router and AT&T service through a place called OTR mobile. This is pretty much my only option for internet. It worked really good (13-26mbps) up until about a week ago. Now netflix is all pixelated, and pausing to buffer. Also while my xbox was trying to download a game, i was watching the speeds as it was downloading. It took a little longer then usual to start downloading. Once it started the download it would go from 500kbps to 1000kbps back to 500 the off for about 5 seconds. The people from the company have sent me a signal refresh, I did a factory reset, and I also got a new sim card and followed that up with another factory reset. None of which has helped my problem.