the free credit has a spending limit. if you do not setup a pay as you go account, you will not be billed. if you use up the credit and have not enabled a pay as you go plan, the the services will be stopped.
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/spending-limit
many services can eat your credit pretty quick. use server less resources (database, web app, etc) when possible. use containers instead of VM's.