You can get at the Shopify billing folks by submitting a support ticket via the support portal (here). I would also suggest checking out your invoices section might have some info on what that charge is for. There is a doc on that section of the admin (here)
You can get connected to our billing team via speaking to our live support team on our 24/7 live support portal. We do not have a direct email address to reach out to the billing team.
Our live support can be reached via our support portal here. Simply select the relevant topics until the live support options appear, you will then be connected to a live support agent. I trust this helps, thank you!
Phone support is not always available, Async and chat are our most efficient and effective channels for quickly and effectively providing support to merchants, this includes ensuring you can get quick access to resources and other support teams. Thank you!