This applies to a galaxy s6 active, but may apply to similar phones. Tried all of the other suggestions first and both ting and T-Mobile customer service first.
I was trying to set up notifications without visual voicemail. Since nothing else worked I decided to try with visual voicemail, so I enabled it. I had done that before but got an error message suggesting that I had to set it up on the carrier's end. This time, before I got that far, I got a message saying that T Mobile has updated their app. I went onto google play and updated it and installed it. When I tried to run it, it still hung at the same spot, so I checked the apn settings. They had switched back to mvne wap without proxy, or I had done so in previous troubleshooting.
I switched back to ting data and restarted. It works now. Didn't have to actually complete the visual voicemail set up either.
There are two different visual voicemail apps in my app folder now. I believe that since the phone was originally an ATT phone, the stock app was interfering even though I had turned off its notifications, disabled it, and even force stopped and disabled it. Installing the T-mobile versions seems to have taken back or released whatever setting was being hijacked by the ATT Version.