How can I find out what I am being charged for?

Question

I have been using the Google time zone, geocoding, and distance matrix API's. I was charged $0 for many months and then all of a sudden $400. I would like to understand why. What I need is a report covering each month for the last 6 months that for each month tells me the service (which API), how many API requests occurred, and the total charge. Is there any way for me to get a (basic) report like this? If not, is there even any way to get the data?

Thank you!