Hello @Chris - Welcome to Microsoft Q&A community forum!
As you have mentioned, you have been using Azure for student sponsorship subscription and able to create resources using the $100 credits. However, the newly created subscription that has email with different subdomain is not active yet.
You might want to check if there was an email notification received for subscription re-activation. If yes, you will be able to continue using Azure for student for another one year.
Will I be billed for this despite having no payment methods attached?
No.
Please refer to the FAQ page - https://azure.microsoft.com/en-in/free/free-account-students-faq/ might be helpful.
Feel free to reply if you have any further questions in this matter.
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