You must first cancel any subscription automatic renewal (if you simply delete an app this does not cancel subscriptions):
View, change, or cancel your subscriptions [subscription automatic renewal] - "Your membership or subscription might renew if you don't cancel your membership or subscription more than 24 hours before your renewal date." At this stage the renewal is considered a purchase. Canceling a subscription does not automatically start a refund since the existing subscription will normally continue until the end of its term and then just not renew. - https://support.apple.com/HT202039
Now review:
Report A Problem to "Sign In for help with iTunes purchases made in the last 90 days" or ask for a refund. Click on this link --> http://reportaproblem.apple.com
For subscriptions, "The Report a Problem website shows most subscriptions, except those for Apple services and iCloud storage charges." [https://support.apple.com/HT201382].
If Report A Problem does not work for a subscription refund you may have to make a special request using one of the contact links below.
Contact iTunes Support:
https://www.apple.com/emea/support/itunes/contact.html
https://support.apple.com/country-selector/itunes