For iOS:

Apple handles all refunds and cancellations for Gather subscriptions and other purchases on iOS devices. All refunds are granted entirely at the discretion of Apple.

To request a refund from Apple, contact iTunes Customer Support directly at https://getsupport.apple.com/.

For instructions on how to cancel your subscription through Apple, see this support article: http://support.apple.com/kb/ht4098.

For Android:

The fastest way to get a refund for a subscription or other purchase on your Google Play account is to request it directly from Google. You can find instructions at Google's support page: https://support.google.com/googleplay/answer/7205930.

For instructions on how to cancel your subscription through Google, see this support article: https://support.google.com/googleplay/answer/7018481.