I am only planning on using the Translator service and from what I see here
https://azure.microsoft.com/en-us/pricing/details/cognitive-services/translator/
as long as I do not exceed 2 million characters a month, I will not be charged for anything.
That being said, is there a way to only have me locked into the free model such that IF I accidentally reach the 2 million character limit a month, then I will be automatically denied access to the service?