How do I connect tmobile home internet to AT&T Uverse TV

I believe U-verse is a service that’s only offered via AT&T’s own internet service (DSL or fiber).  If you no longer have the AT&T service, then you’ve lost U-verse. Even if you start AT&T internet again, you may not be able to get your old U-verse service.  AT&T discontinued that recently and replaced it with AT&T TV--old customers could keep U-verse, but new customers have to use AT&T TV.

OK, I need to correct part of my answer. It is possible to have U-verse TV over another ISP (as were doing via Comcast).  I lost U-verse TV when I cancelled AT&T Internet service, because they cancelled both services (TV and internet). When I cancelled AT&T Internet, the agent who helped me told me I couldn’t keep the U-verse TV.  He apparently was either misinformed or misleading me.  If you kept your U-verse TV account current and they haven’t cancelled it, you should, theoretically, be able to use it with T-Mobile Home Internet. I’d contact AT&T customer service to have them help you get it connected again.  

As far as I can determine, you should leave the AT&T gateway hooked up exactly as you had it before, and all you should change is to disconnect the ethernet cable going into the Comcast gateway from the AT&T gateway, and plug that into the T-Mobile gateway, taking the Comcast gateway out of the system. Essentially, you’re just replacing the Comcast box with the T-Mobile box. Everything else should have remained as it was.  It sounds like you may have changed more than just that. AT&T ought to be able to help you figure it out.