How can I tell if I’m enrolled in automatic debit?

Go to Billing > My invoices.
Open a pending invoice.
Check the payment method and the notices shown in the summary.

Current summary of a pending invoice — The details let you verify the payment method associated with the invoice.

If there is no clear indication of a recurring charge, do not assume the debit is active. Check it by submitting a ticket to Customer Support before the due date.