App Service instances have to be deleted, or the cost accumulates. The FAQ already covers that, https://azure.microsoft.com/en-us/pricing/details/app-service/windows/#faq under "Am I charged for apps while they are in stopped state?" The database usage follows a similar rule, as even you were not using the instance, the related resources have been allocated and charged under your subscription.
Like explained in "Upgrades and spending limits" section, you need to upgrade to Pay As You Go subscription when credits are all used and that requires a credit card in many countries,
https://azure.microsoft.com/en-ca/pricing/offers/ms-azr-0170p/