I think these days for privacy reasons mobile OSs make this intentionally difficult to obtain. It might be easier to find a different way to do this, such as requiring a login and using that to restrict access where necessary.
I already have a login and registering new username system but i didn't add confirmation on email because most of the users gave up when they have to go in email and confirm email and the majority are not bad intended :), one version of my app is already on google play and now i need this for an update, some users exploited some bugs from a 3rd party API trough my app on witch i dont have control when i ban them, they create a new username and so on. I have made use of local storage to bind the phone to one account and restrict the creation of multiple accounts but if the app is uninstalled and installed again local stored keys are lost