Hello Joshi Prayag H,
Thanks for your question.
To reactivate you will most likely need a billing support ticket. The steps to check why and reactivate are here: https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/azurestudents-subscription-disabled
To create the billing ticket, See: https://azure.microsoft.com/en-us/support/create-ticket
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Regards,
Abiola