Hi,
With Azure Free account the $200 credit is only valid for the first 30 days. At the end of the 30 days, you must upgrade to Pay-As-You-Go account. Once you upgrade, if you only use Free services and stay within limits, there will be no charge during the remaining 11 months.
Article below will help you avoid charges:
Avoid charges with your Azure free account
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/avoid-charges-free-account
Create services included with Azure free account
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/create-free-services
Please add a comment below if you have any question or if something is unclear.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP