Hi Kaenia,
#1 Ensure you visit the following page to activate your Student Offer:
https://azure.microsoft.com/en-ca/pricing/offers/ms-azr-0144p
#2 I'd recommend you contacting GitHub support to see if they can assist you with verifying your student status.
Try posting in the community where someone from Github can assist:
https://github.com/orgs/community/discussions
#3 Try opening a Billing support ticket with Azure:
https://azure.microsoft.com/en-us/support/
If this is helpful please accept answer.