1.You can try to reset your Network, for that go to:
Settings>System>Reset options>Reset Wi-Fi, mobile & Bluetooth
2.If still you encountered the same issue after trying previous steps then you can try to "Factory Reset" your device.
Settings>System>Reset options>Erase all data(factory reset)
*Please note that once the Factory Reset is completed, all data, apps, settings and personal information will be deleted.