some possible solutions I found in regards to your problem are:

If you are unable to find usage stats, try using the command line interface in google cloud to view/set up logs:
https://cloud.google.com/logging/docs/reference/tools/gcloud-logging#getting_started

Looking at quotas:
https://developers.google.com/maps/billing-and-pricing/manage-costs#quotas
- It states that when your project reaches the quota limit "your service stops responding to requests", are you sure that your limit is properly set up? Compare how much you got charged to the pricing https://developers.google.com/maps/billing-and-pricing/pricing
- You can set up alerts (both usage and budget) at points where you haven't used up all your free usage to figure out at what rate your api calls are being used (i.e. 1000 map loads)