The first thing to check is if you have any subscriptions through Roku. Log into your user account (https:\\my.roku.com) and click "manage your subscriptions". If you don't see anything there, you are not being billed by Roku. If there is something there, that's probably what you're being billed for. Warner Media is what people will see on a CC statement for channels such as MAX (formerly HBO Max).
If there's nothing listed under subscriptions, you are being scammed. It isn't Roku billing you, regardless of what the statement says. Scammers have stolen your CC information and submitting charges to your card. They can enter anything they want to say who the charge is from, so they pick something they know is a valid name. You need to contest the charges, and immediately ask your CC issuer to cancel your card and issue you a new one. If your CC information is out there, someone else will come along and use it as well.