Check this lock removal service. Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).
Your Apple account is likely okay since it was you who did all the ID changing. I presume you did not send them your ID or password. If you still have concerns:
Click on this link "If you think your Apple ID has been compromised" --> https://support.apple.com/HT204145
'Checklist: If you want to see if anyone else has access to your device or accounts' click here --> https://support.apple.com/HT212021
Security and your Apple ID - https://support.apple.com/HT201303
Contact Apple for help with Apple ID account security - https://support.apple.com/HT204169 "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues." Better for directly reporting an issue.
