Are you sure it is for a subscription you have? I somebody shares your account, or your card, or you are a Family Sharing Organizer, it could be another person's subscription.
Do you have more than one Apple Account?
You say you are not using an iPhone but I am not sure how that applies to this situation. You don't need any Apple equipment of any kind in order to have a subscription. You can cancel online --> https://support.apple.com/121290
If you truly cannot find this subscription then contact Apple:
Refer to this page for Apple Support features ➔ https://support.apple.com/contact
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page under “Get more help” (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This support article has various country telephone numbers for contacting Apple for support and service ➔ https://support.apple.com/106932 Scroll down to “Connect with live support”. If your country is not in the list, go to the “Other countries” entry at the end of the list and click on the “options” link. Not every country has telephone support, and phone numbers may only work when calling from the same country.
