Honeywell wifi thermostat not able to connect

Of course T-Mobile support points their finger at the device and not the gateway.  I tried several iterations of WiFi networks within the T-Mobile gateway, but could not connect my EcoNet device.  I have a cheap Wavlink extender for my backyard that connects to the T-Mobile gateway that my EcoNet can see.  EcoNet connects fine to this extender.  My T-Mobile service is great, router is quite poor in options, local connectivity, and standards.  Likely, I will ultimately connect a real WiFi router to the ethernet port of the T-Mobile gateway and shutdown the WiFi on the T-Mobile.  Can use conventional WiFi router and extenders or spend more and put in mesh network routers.