iPhone Activation Lock after update

I assume you purchased the device used and the device was not properly reset before it was sold to you. Only the original owner can remove the lock. If the original owner is not available, then the device will not be usable. Apple does not get involved in third party sales.

If you purchased from Apple or Authorized Apple Seller, then submit the original purchase receipt here and the lock will be removed.

https://al-support.apple.com/#/al/agreement