Ryder here, from the Social Care Team at Shopify. Thanks for posting - I'd be happy to see how I can assist you today.
If you've confirmed that your shop is in fact closed, then you will no longer be invoiced for your Shopify subscription or third-party app charges. You can find more information on that here.
I'm sorry to hear that you've decided not to move forward with your growing your business on Shopify. Should you ever decide to try again, please note that our Support Advisors are staffed 24/7 to aid our merchants with both technical questions as well as business coaching through our Contact page. You can also get in touch through Facebook Messenger or Twitter direct message.
Do you mind my asking why you've chosen to close your shop? Were there any entrepreneurial obstacles that you were facing that I might be able to assist you with?