Log into your Roku user account (https://my.roku.com). You can see any subscriptions you have with Roku there. See if it's listed there, and confirm you also have it through Amazon. Then remove one of the subscriptions.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.