LS300 not reachable by ethernet or cellular

I have 3 LS300 modems, set up with AT&T cellular service. One of the modems stopped connecting exactly at the time that my monthly cellular plan renews (midnight of the renewal date). I have not been able to connect to it since by internet or direct ethernet connection.

I have it in my office now and I have done many manual reboots and several full factory resets. I am not able to access the router at all. I am connecting directly to it by ethernet and querying No response. When I do the same with one of the other modems, it connects no problem.

Any suggestions?

I would check to make sure your computer has a address as the gateway. If it does i would try to telnet into the modem using on port 2332 to verify that we can access the modem.
If you can access the modem there should be no reason why we can’t access AceManager.