Activation lock

See Turn off Activation Lock https://support.apple.com/en-us/HT201441. 

If you have iOS 11 or later and your account is protected with two-factor authentication, use get help with a forgotten passcode or disabled device to recover your passcode. Otherwise, use forgot your Apple ID or your Apple ID password to recover the needed credential(s). If you can’t recover the needed credential(s), contact Apple Support and present your original purchase receipt for your device from an authorized Apple seller with the device’s serial number on it. You’ll need a photo ID too.If you can do neither, then the device is useless to you.

You can use the suggested support options below if you have the needed receipt. Alternatively, if an Apple Store is open in your area, then you can go there to deal with your problem. In this case, you can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if you want.

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitter https://twitter.com/AppleSupport

Apple ID account security for country-specific andregion-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.

Use Apple's iForgot service, or contact their Account Security team, or if you’re the iPhone’s original owner, supply Apple with its purchase receipt and ask them to remove the lock.

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