You can try checking your purchase history to see if you'll be able to view your Hulu bill there. Visit this link if you need assistance on how to check your purchase history: How do I view my purchase history?
Moreover, if you need further help, it may be more effective to get help from our Billing team. You can contact them here: support.roku.com/contactus then choose 'Questions about my account or billing' on the drop-down menu. They are the best ones to help you out with that matter.
For account and billing related issues, please reach out to our support team directly here for your 'Account or billing' issue, here: https://support.roku.com/contactus. They will be able to further assist you.