iPhone blocked after logging in someone else's iCloud
I put the phone up for sale, on the ad platform, after which a girl wrote to me asking me to go to her iCloud, I went in and after that the phone was blocked.
[Re-Titled by Moderator]
iPhone 13
Question marked as
I'm sorry to hear you were scammed. Since you are no longer signed into this iPhone you'll need to submit proof of purchase to show ownership of the iPhone using the Start a support request section at How to remove Activation Lock - Apple Support
You've learned a valuable lesson. Never allow someone else to sign into your device with their Apple ID.