Q: how do you know if unlocking your phone worked?

If the phone has been officially unlocked, iTunes will notify you when you connect the phone that it has been unlocked.

You can also try to insert a SIM card from another provider to find out.

Putting the SIM into a new iPhone does not affect the unlocking process for the old one.

You can still get the old phone unlocked, if unlocking is supported for your device by your carrier. If you still have no confirmation from them, ask them again, sometimes it takes a little longer to process an unlock request