Two possible solutions:
Get the old ID working again so you can remove the Find My setting. If a message says your Apple ID is locked or disabled "for security reasons"", the document If your Apple ID is locked or disabled - Apple Support directs you to reset your password as outlined in this article --> If you forgot your Apple ID password - Apple Support
If you use two-factor authentication and can’t sign in or reset your password, you can regain access after an account recovery waiting period, as outlined in this document: How to use account recovery when you can’t reset your Apple ID password - Apple Support
However, you may be using the terms "disabled" somewhat loosely in which case you need to tell us exactly what was done or any error messages you see.
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). Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support