My ATT carrier said they could no longer unlock phones and that I would have to do it through here. I have already erased my phone

There's multiple kinds of "locking" on devices. Click on the links below to find instructions on how to deal with your specific situation:

1) iCloud: Activation Lock - https://support.apple.com/HT201365 - This is a security feature so only legitimate (i.e., not stolen) redistribution of devices is possible. See: 'How to remove Activation Lock' --> https://support.apple.com/HT201441 - If an activation lock was put on a device, only the owner of the account that applied the lock can remove it. Get them to remove it or return the item for a refund. If you are the owner, see the part at the end about asking Apple to reset the device.

2) Device lock: "If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled" click here --> https://support.apple.com/HT204306

3) Carrier lock: Read this link on "How to unlock your iPhone for use with a different carrier" - http://support.apple.com/HT201328 - Only some carriers offer the ability to unlock iPhone for use on any carrier. Follow the instructions in this article to unlock your iPhone.

Unlock what?

The carrier lock? That's through AT&T.

Your device? You've already erased it.

Are you giving it away? Follow these steps: https://support.apple.com/en-us/HT201351