You can find more details on your billing here. If you have questions regarding how Parsec charges you for cloud computers, please take a look at this article.
There are also a couple confusing parts of Parsec's billing.
DATES LOOK WRONG ON BILLING RECORDS
First off, we measure time in "UTC" so that our computers all over the world are synced up. Currently, our billing is also in UTC, so it's not time-shifted for you in that graph, so it could be that you are seeing billing on days you don't expect for that reason.
MY BILL CHANGED
Secondly, we don't get billing data from Amazon immediately, we run processes in the background that updates our understanding of costs from Amazon that happen independently of you starting and stopping your machine. Sometimes these can be time-shifted, so you'll get billed on dates that you didn't actually use your machine because we didn't know about the billing until then. What you see in this graph is a rolled up version of that data, and as such it can be confusing. This is obviously not ideal and we are working on building a better, more intuitive usage and billing UI that shows off your actual usage better.