I have an iPhone 8+. Initially, I simply forgot the passcode, so I tried to restore the device; however, it became locked because I also forgot the iCloud account details. The problem is that I no longer have any of the associated information—such as the email address, password, phone number, or even the original receipt—as I purchased the device abroad back in 2010. I only have the box and the device itself.
[Re-Titled by Moderator]
Original Title: Activation lock