The reason you can't find your AskNebula website subscription in your phone's settings or manage it through the Play Store or App Store is that this type of subscription is exclusively for the AskNebula website. It operates through web browsers like Google Chrome, Safari, etc., and is not connected to any mobile app store systems.
Since it's not an app-based subscription, it won't appear in your mobile device's subscription management settings (such as in Play Market or App Store). Instead, it’s tied to your account on the AskNebula website.
To cancel your AskNebula website subscription, you will need to follow the instructions provided in this article: How to cancel a subscription?