You can access your Comet billing history and active charges, as well as log in to your Comet-Hosted Server and raise a support ticket in your Comet account: https://account.cometbackup.com.
Not to be confused with the Comet Server, you can think of this account as your Comet ‘billing and admin’ account. Comet charges devices and boosters on a 30-day basis, and these fees are calculated and charged to you real time. You will not receive a lump invoice at the end of the month.
For more information on how billing and payment works at Comet, check out our guide on Managing your Comet Admin Account.