See details of the offer:
This offer is limited to one Azure for Students subscription per eligible customer, is non-transferable, and cannot be combined with any other offer unless otherwise permitted by Microsoft. Azure for Students has a limited supply of activations and the offer is available only while supplies last.
https://azure.microsoft.com/en-us/pricing/offers/ms-azr-0170p/
Is there any specific message/error you get regarding this?
You can reach out to global support for assistance on specifics - https://support.microsoft.com/en-gb/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola