Hello haeleeholland,
From your post we can see that you've found both your Hulu and iTunes Store accounts were compromised. How scary! You've canceled your Hulu account and want to know how to untie it from your iTunes Store account.
Was the subscription through the App Store? You can use this to check your subscriptions: How to cancel a subscription from Apple. If you select the blue "Cancel a subscription" button, it will get you right to the spot to check to see if Hulu is there and your other subscriptions.
We'd also suggest to go through this guide: If you think your Apple ID has been compromised. Go through each section and focus in on the section " Gain control of your Apple ID". You've mentioned that you've changed the password and that is awesome! You'd also want to see which Apple ID is under Settings > [your name] > iTunes & App Store to verify this as well.
Take care.