Did you choose the reset that saves your data? If so, this could be your problem. You may well need to "Hard Reset" the device, which will wipe everything. Otherwise, most devices do need a data or WiFi connection to complete installs.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the phone...
1. Make sure that the phone is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together, until you see the...