Sophia here from Shopify.
Once three payment attempts have been made on your Shopify invoice, the account moves into a frozen state and you won't be charged further for your Shopify subscription. It can just be left alone as an inactive account at that point if you don't wish to continue with it.
You may still see a third-party app charge come through separately depending on the billing period for the app. For this reason, it is advised that you uninstall apps before closing your store (or otherwise leaving it inactive). Since your store is already inactive, I recommend contacting the app developers for any paid apps you had installed to see if they can cancel future payments, particularly if you installed any apps that requested your payment information outside of Shopify.