One-time purchase means you pay once for the package you pick. It is worth confirming.
A one-time purchase should not renew or ship again on its own. The page says it is not a subscription, which is a point in its favor compared with auto-ship models.
We do not process orders, so the official checkout is where this is stated and enforced.
On the checkout page, look for any tick box about repeat shipments. Check your confirmation email, and your card statement a month later. If you see an unexpected charge, contact the seller in writing and your card issuer.