You can try cancelling your HBO Max subscription directly on your TV screen. To do this, follow the steps below:
Press the Home button on your Roku remote.
Highlight the channel you wish to cancel using the directional pad in the center of your Roku remote.
Press the Star button on your remote to open the options menu.
Select Manage subscription to view the renewal date and access additional options.
To unsubscribe, select Cancel subscription. A message will appear confirming the duration of continued access, content, and services.
When prompted, select Cancel subscription. Roku will display a message confirming cancellation and your last day of access.
If still no dice, 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.