iphone factory unlock - NO SIM

I completed my 2 years contract with AT&T and unlocked my phone by following the steps available on Apple website

1. Ensure that you've waited the recommended wait period provided by your carrier.
2. Back up your iPhone.
3. Erase the contents of your iPhone.
4. Swap the old SIM card with the one for the new carrier.
5. Complete the setup assistant and restore your backup.

At the 5th step when I tried activating my new SIM through iTunes it says "Sorry we could not activate your iphone at this point of time". I checked with Apple and they confirm that it was unlocked successfully but still cannot read new GSM SIM. NO SIM is displayed on iphone screen. Itunes, iOS everything is up to date.

Please advise.