Hmm, that's super odd.
Are you sure it's coming from the T-Mobile App and not another application? You could try updating all the apps you have installed to see if the notification goes away. Another thing you'll wanna try is force stopping and even uninstalling/reinstalling the updates for the Play Store app itself. Please come back and let us know how it goes. Thank you.
Hey there! I just wanted to reach out and see if you'd had a chance to try the troubleshooting steps Mike recommended. How is everything going with your tablet?