You probably have received a message leading you to your group usage statistics and a group management interface.

Usage statistics

Among the files in your directory, you can find the following:

Invoices will be sent quarterly for the amounts in the following files: invoice, premium, commitment

Group administration interface

The second link in the message you have received will take you to the list of users in your group. More information about the interface can be found here.

Live usage report - Commitments

For the groups with Commitments it's possible to look at the live usage:

It shows an estimate of the current consumption as well as the expected usage based on the Commitment amount for the period it relates to.