Subscription refund

Strictly speaking all purchases are final (after all, you can't very well return them): please see this page for information on requesting a refund: Request a refund for an App Store or iTunes Store purchase - Apple Support

However Apple have been known to be sympathetic in cases of actual error, so it's possible that they may allow you a refund as a one-off concession: but please be aware that they are under no obligation to do so: go to iTunes Store - Contact Us - Official Apple Support

Alternatively go to the page suggested in the Help page linked to above: Report a Problem

You can actually check the website reportaproblem.apple.com to check for your refund request. I've tried that myself and it worked, however I think it's case to case basis.

I see. You might want to contact iTunes via get support.apple.com to schedule a callback and check for options.