As told to you when you requested deletion of the AppleID, if you did not sign out before the deletion request was processed, then you cannot do so afterwards and your device will be renedered useless to you.
There is no fix and nothing Apple can do about it now that the AppleID has been deleted. Other posters in the past have confirmed that fact. If you did not sign out before the AppleID was deleted, as instructed, your device will be useless to you, and there is no fix for that situation. You cannot sign out because the AppleID no longer exists in Apple’s system to authenticate to, and Apple cannot restore that AppleID now that it has been deleted.
How to delete your Apple ID account - Apple Support
- ”Make sure that you sign out of all your devices to avoid issues with apps that use your Apple ID account or iCloud. After your account is deleted, you can't sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted.“
“What happens if I change my mind after I have requested that my account be deleted?
While your request is being processed, you can contact Apple Support with the unique alphanumeric access code you received, and we’ll help you cancel your request. After your account is deleted, Apple can't cancel the request, reopen your account, or restore your data.”