Have you checked your junk/spam folders for your student email? Often the codes can end up in there depending on your client's security.
I can't send the promo codes from my end, but please email firstname.lastname@example.org with a scanned copy of your current Student ID or enrolment letter and they will send you your promo code.
Try logging in using office365 page rather than outlook (once credentials have been entered it will ask you if it is a work/school or personal account) ... or alternatively unlink/link your student email account to your phone’s mail app...
dont forget to make sure you’ve added your student email as your email in your optus account settings/preferences:)! Set it as the primary email, get your code, complete order then list student email as the alternative email 🙂