my iphone5 has hanged while loading new ios. i can't do anything with it. Apple chat and online support needs serial number. HELP

The serial number is engraved on the back of the phone:

See this document on how to find it: See iOS: How to find the serial number, IMEI, MEID, CDN, and ICCID number

If your iPhone is stuck in updating, try to restore it using iTunes: See iOS: Not responding or does not turn on

If that does not work, force the iPhone into recovery mode to restore: See If you can't update or restore your iOS device