How to unlock an iPhone 11 from iCloud account

Contact the previous owner.

The previous owner will have to release the lock, or you will want to request refund your purchase.

Until and unless the person holding the Apple Account associated with Activation Lock releases the lock, or provide you with an original purchase receipt from Apple or an Apple authorized reseller, it will forever be useless to you.

If the seller is has disappeared and as is too often the case, you got scammed. Recycle it. Yes, really. Recycle it.

The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community

You won't be able to unlock the phone without the previous owners assistance. Activation Lock is a theft deterrent feature that cannot be bypassed. What you described is no different than what would happen if someone took your phone without your permission. It would be no use to them either.

In order for the phone to be usable the original owner should Factory Reset it, so if you cannot contact them, it will remain a brick. For all you know, the seller is not even the original owner and may have sold you a stolen device.

You won't be able to use that iPhone; the activation lock is an anti-theft measure. If you bought it through a store or website, ask the staff for a refund.

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