You can navigate to your Roku account here to see your subscriptions after you login to your dashboard.
https://my.roku.com/account/subscriptions
If you have any disputes or questions then you need to navigate here and select the Billing options from the dropdown menus.
https://support.roku.com/contactus
When you are in your dashboard, enable a PIN which will prevent any future Subscriptions or Channels from being installed without you first entering your pin on a popup box on your Roku Device.
Also, seems some people have been receiving fraudulent invoices for services. Check your subscriptions and include any such info to that Roku support contact form.