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You need to go to the Azure portal and note your billing account, subscription ID, and invoice numbers and verify the spending limit is ON for the student subscription or stop all resources if it shows pay as you go and delete any running services or marketplace items, and set a 0 budget alert because the expedited refund limit reached blocks self service,
Then create a support request and attach screenshots of invoices, cost analysis (last 30/90 days) and subscription details.