I have an AT&T prepaid sim card and the 100 gb for $50 plan. I bought a Netgear LTE modem LM1200 from Amazon and a Netgear AC750 WiFi router model R6020 at Walmart. The sim has been activated. I have a good signal. The modem connects to the internet. I cannot get any websites to load on any device. They either timeout or return error the website can't be found. I know just enough about networking to screw things up. What am I missing?