Cannot unlock phone after update

When you said not brand new, I believed that was in relation to my question asking if you bought the phone brand new originally?

Since you are the original owner, you'll need to follow the directions in the link I provided which is this --> If you forgot your iPhone passcode - Apple Support

I know it's your phone. I didn't know if you bought it brand new originally?

If the passcode has been forgotten, you'll have to follow the directions in this link to erase your phone using a computer with iTunes (Windows) or Finder (Mac) --> If you forgot your iPhone passcode - Apple Support

You can use the directions in the Related Article Link at the top of this page, which brought you here, if you see the Unavailable Message on your iPhone.

And once you have erased the phone, you can set it up again from your most recent backup.

That's why I wanted to know if you are the ORIGINAL buyer of this phone. You bought a used iPhone, which was NOT prepared properly for a new owner. And you have run into a significant issue, which may render the phone completely useless to you. You very likely do not know the Apple ID and Apple ID Password which was used to set up this phone. Without that information, you can't restore the phone unless you can reach whoever you got the phone from and they either remove the phone from their account or give you their ID and Password. Without that, you can't use the phone. Apple won't help you unless you possess the original purchase receipt with the iPhone Serial Number printed on it. And we can't help you. There is a HUGE risk to buying used iPhones, iPads, Apple Watches, etc.

I wrote a user tip about doing just that --> The All Too Common SAD Reality of Buying … - Apple Community

Unless you can reach the original owner of the phone, I think you should be prepared to buy a new iPhone.

Then schedule an appointment at your Apple Store Genius bar for direct help from Apple. But don't even try today. There are huge lines outside just about every Apple in the world today as today is new iPhone launch day.

Here is a link you can use to schedule an appointment --> Genius Bar Reservation and Apple Support Options - Apple

Are you the original owner of this iPhone?