iPhone is locked and it won’t recognise my Apple Account

iPhone 11 entered Lock mode after I tried to Factory reset it, because it keeps saying invalid account whenever I try to input my account and password, and I had no idea what that is. And now Its locked and it won’t recognize my account, saying wrong password or apple account. I contacted Apple support and I filled out a form and they asked for “proof of ownership” which I entered as the sales receipt I got from my reseller. But Apple won’t still can’t process my request. I bought the phone second hand and from a different city in my country. I have the box, the phone, the phone number on my email/iCloud and also my email logged in on this device I’m currently using. Please how can I resolve this issue, or is the phone gone for good as some are saying?

[Re-Titled by Moderator]

Original Title: Locked iPhone