@SuvasishPaul Not that it solves your problem, but to rename the devices correctly you could try 2 different options.
1) Send a notification to the device, with a reference code for the user to send back like a pin and then it confirms the user of the device of just ask them to call you, but you would only be able to do one at a time, otherwise you would lose track of who is calling from what notification.
2) Depending on your users and environment, you could lock their device. I would hope they call you and don't wipe their phone first.