Unable to verify my email address (Apple ID / iCloud)

I've been prompted to verify my email address while trying to sign in to my iCloud account through a server. "Your Apple ID email address must be verified before you can sign in. Verify the address below or choose a different address to use as your Apple ID."

When I enter my email address it says "This email address is not available. Choose a different address." and doesn't have any prompt for the next steps... I don't have another iCloud account to enter.

Any help would be appreciated.

Thanks