Q: Help! Everything is gone!

You need to contact Apple account security: Contact Apple for help with Apple ID account security - Apple Support.

You need to use the old e-mail again as your Apple ID and password.

Content is forever tied to the Apple ID that was used.

I think you're saying you simply changed your Apple ID.  Have you signed out of every device using the old ID?  Follow these instructions very carefully.

Change your Apple ID - Apple Support

Yes you can change the Apple ID see the link from sberman post.

If you change Apple ID in other ways the statement I've made is valid.

Go to https://appleid.apple.com/#!&page=signin and log in with your (old email?) Apple ID  I assume that you still have the password.  This will get you "unlocked"

Your appleid is the key to your data.  You need it to be tied to a real email address. You really need to keep that email address active. You can change that email address.

Change your Apple ID - Apple Support

Do not panic you will get it fixed up!