Ryder here from the Social Care Team at Shopify. I'm sorry to hear about your experience, and I appreciate you bringing this to our attention. Once you close your store, you may be prompted to pay any invoiced outstanding charges; however, this would happen immediately - not several months later. Is there a possibility that you had created multiple accounts, or gave permission to a friend or family member to use your credit card for their shop? You can confirm this by entering any email addresses you have here to receive an email listing all the associated .myshopify.com URLs.
If you're sure that this charge wasn't from any open shops, please contact our Support Team so we can take a closer look at where this charge may have come from. We'll be privately requesting a screenshot of the charge in your bank statement with the 8-digit invoice number. Charges invoiced by Shopify will appear as Shopify * XXXXXXXX. If this charge took place through PayPal, the 8-digit invoice number will appear in an expanded view of the charge within the PayPal admin account itself, typically towards the bottom.
Once we've received that screenshot from you, we can take a look at what information we have on our end in relation to your account and advise you of the next steps. Hope this helps! Please let me know if there's anything I can clarify.