The email modification can be done only from the support, validate with them what is going on
You can chat in direct
• Sign into your account
• Follow the link on this page: https://fizz.ca/en/faq/im-unable-log-my-fizz-account-what-do-i-do
• Wait 3 seconds for the green bubble with a '❔' appears at the bottom right of the browser, if you use a phone you must use it in desktop or horizontal mode
• Choose the option 💬 chat
• If the green bubble does not appear make sure your ad blocker is disabled, otherwise try with another browser.
Or by private message on Facebook: https://www.facebook.com/fizzca/
Indeed, email address is changed by support usually.