If you no longer wish to keep your Shopify store active, then you will need to close the store to remove yourself from active billing. You can close your store by logging into your store through Shopify.com. Once there, you'll need to navigate to Settings/Plans and Permissions and select "Close Store" at the bottom of the page. If you follow the prompts then this will ensure your store is closed and removed from active billing.
That said, while our Terms of Service does state that we do not provide refunds; however, we can provide refunds in a case by case scenario as long as the store is fully closed. I have sent you an email titled "Shopify Forum Support" to verify your store. If you can close your store, and reply to my email then I can review your refund request.