You can review what exactly caused the cause and the billinbg cycle. To do this:
Search for Cost Management + Billing section in the Azure Portal.
Review your Billing History and Usage Details to identify where the charges are coming from.
You can then delete and remove the resources by looking for them in the portal.
However, If you want to cancel and delete your subscription, See the steps here: https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/cancel-azure-subscription
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Regards,
Abiola