Actually, the way of charging is not transparent
Actually, the way of charging is not transparent, I don't use it, but I am still charged and cannot find a cancellation.
As this was subscribed to via AWS Marketplace you must cancel a subscription by going to the AWS Marketplaces, then Manage Subscriptions and search for "Barracuda WAF-as-a-Service", then in the top right click on the Actions button and choose Cancel Subscription.