Alert: Your data connection is disconnected.

This is the message displayed on the screen of my Netgear unite 781s hotspot:

"Alert: Your data connection is disconnected." Of course, when I touch connect, it won't connect. In the top left of the screen is where you normally would see the signal bar, 4g LTE. All of that is missing. I've been through the guide for troubleshooting and read everything I've found online even remotely related but can't figure it out. I thought it maybe the apn so I changed it to broadband. Not that.  Then I did a factory reset a couple of times. No help. I tried changing the sim with no luck so put the old one back in. 

I'm at loss as to what to do. Help!

If I can't get this working I'll be getting a new hotspot from att or Verizon. I already have the yagi antennas. Can somebody tell me what models have the inputs for the external yagi antennas? And which has the best internal antennas? I know this is an att forum, but looking for input on both brands to make a better decision.