How do I talk to a customer service person?

From the portion of information provided it simply looks that you are under the 192.168.12.1/home url.That is not a public ip address that lets anyone simply have access to your router information,Its used only from devices within the network to access the cut down admin portal of the router.On a secondary note the firmware your 5g home is using does not allow anyone including your self to do anything to your router as T-mobile started shipping certain routers with firmware forcing users to either use a third party non tmobile application to do anything via their Computer using api’s.T-mobile has gone to using their T-mobile Internet application on your ios or android device for making simple changes to your router.