Billing is the plan you are on and the credits that plan includes. Nothing here is a surprise charge: work pauses when credits run out.
Information
Open Billing from Settings, then Billing.
Starter is free and includes a daily allowance. Paid plans raise that allowance. Upgrade from Billing when you hit the ceiling often.
Usage numbers on the Dashboard are the same numbers as Billing, shown in less detail.
Paid plans ask for a card. Invoices list what was billed. Seats for a team are on the same page.
Warning
If a charge looks wrong, do not retry blindly. Write to Help with the invoice date.