You don't see it when viewing your Purchase History or Subscriptions because it was not one that was made with an in-app purchase or managed by Apple at all. What most likely happened is that you were directed to their website from a Social Media post or Website Advertisement for a free Astrological Reading. The free reading was actually a free trial for their service that became a subscription.
Since Apple is not involved, you will have to deal with that same website for a refund and to cancel the subscription. Look through your emails as this may have happened a month before the subscription charge started. They also have a page here describing how to cancel the subscription:
https://24hours.support-nebula.com/hc/en-us/articles/28900802305297-How-to-cancel-subscription
And their refund policy is available here:
https://24hours.support-nebula.com/hc/en-us/articles/28900464111505-How-to-receive-a-refund
If you are unsuccessful in getting a refund or cancelling your subscription, you will need to dispute the charges with your bank that issued your card.