I merged your threads, since your latest one was a continuation of your original post.
What's the exact message about restricted voice and data? Have you asked your carrier about this? Do you have a plan with unlimited voice and data?
What apk file are you trying to install? apk files can be risky, since the places where you find them often don't vet the files for malware. Since many people try to avoid paying for apps by searching for apk files, they're ripe targets for cybercriminals or hackers. And as
@PJRed2008 mentioned above, if the app you're trying to install isn't compatible on your phone in the first place, that may be why it's not supported.
When do you get the com.android.settings has stopped error? Randomly, or when you try to install an apk?
Does any of this happen in Safe Mode?
https://support.t-mobile.com/docs/DOC-30604