Changing the primary email address on an account (and : What to do after you change your Apple ID email address or password - Apple Support) should not affect any of its purchases - are you sure that you updated your existing account and didn't create a new account, if you look at the account's purchase history on your computer's iTunes does it list the purchases done before 'changing' it ?
Past purchases (those still in the store and, if you've moved countries, not bought before changing countries) should show in the Purchased section for redownloading, unless you've hidden them.
my email provider has closed my email address. i have a new email address and have changed my email address in my apple id. i now am unable to access purchases that i made before the change. how can i retrieve all my music?
