Unfortunately, to use Azure services - you need a Credit card.
Even if you are using Free services:
[https://azure.microsoft.com/en-us/free/
The credit card is used during the sign up process, to check that you haven't got multiple tenancies/subscriptions created for Free and if any resources are Pay As You Go - then the credit card gets charged - so budget alert and resource tracking and cleanup is key.
The $100 credit for Students, is for 12 months, after which it switches to Pay as You Go and then you have to resubscribe: [https://aka.ms/azure4students
[https://learn.microsoft.com/en-us/azure/education-hub/azure-dev-tools-teaching/program-faq#azure-for-students