My dad forgot his iPhone 4s Passcode so I placed it into recovery mode and reset it, the bad thing was that it was locked with a old iCloud account that nobody in our family knows and now the phone is stuck on the iCloud Activation Screen. I can prove that the iPhone belongs to my dad. Thanks for your support!
Extra - When I reset it, it updated to iOS 9.3.5.
iPhone 4S, iOS 9.3.5
Tthere are alternative ways to recover and/or change the Apple ID and password, but they all involve knowing something about it. Start with this link and see if you can use any of these methods.
Apple ID - Official Apple Support
If none of them work, having ownership proof is helpfull, but you'll need to make a Genius appointment at the nearest Apple Store.
We do not know the email address, unfortunately!
Did you try the 1st link and click Forgot Apple ID?
There is a contact link.
Ok, I tried the 1st link and clicked forgot Apple ID but remember, the email is unknown! I may try the contact link when I get back home from school.
Unfortunately I can not contact them as I am not available in any of those time slots, I can still prove that the iPhone belongs to us.
If you are the original owner, take the phone, the original purchase receipt, and a photo ID to the nearest Apple Store.
If you have the documentation that proves your Dad is the original owner, you can contact Apple and submit that to them. After verification, they may be able to remove the activation lock from the device.
Otherwise you have no solution.
iPhone 4S Stuck on Activate iCloud Account!
