I want to cancel and refund my subscribtion

To cancel a subscription, go to:

Settings → Apple ID → Subscriptions

Select the subscription you would like to cancel, tap in and select "Cancel Subscription" If you are in the middle of a period, you will have access to subscriptions until it expires. After that, the subscription closes permanently.

After your subscription has been canceled, you can see how to request a refund here:

Request a refund for apps or content that you bought from Apple - Apple Support