I see that you're new to our T-Mobile Support Community, welcome!
I haven't seen many reports of the Note 4 essentially being useless after the latest software update. From the sounds of it, you have tried all of the troubleshooting steps that we would've recommended along with Tech Support. At this point, you're likely looking at a warranty exchange. Do you know if your Note 4 is still under warranty or extended warranty? If so, you can Contact Us to set-up a device exchange.
I had the same issue and none of the trouble shooting suggestions worked. Here's how I resolved it. Go to the app store and download an app by the name of Wake Lock. When you open the app, select the Partial_Wake_Lock. This might drain your battery a little but the phone will function normally. If you have to restart your phone by any chance, make sure the app is functioning.
Keep in mind the Note 4 may be one of the impacted device models for the U1900 network upgrades. If your device is impacted you may experience 2G/EDGE speeds and never see higher data speeds due to these upgrades. I hope you are not one of those impacted customers, but this is just a heads up of the possibility.
Vincent I've been experiencing the EXACT SAME problem! Soooo frustrating considering I just finally paid off the phone. Glad to know I'm not alone - I joke that I repel technology and was beginning to think it was actually true!
Thanks Amanda for your suggestion of checking the warranty!