This is an accepted solution.
Ted here from Shopify, thanks for posting your query!
I'm sorry to hear you closed your Shopify store. How did you find the platform?
I was taking a look and it appears as though ProveSource issue their invoices directly and not through Shopify. I'd recommend contacting their customer support (firstname.lastname@example.org) and asking them for a refund. If they require proof that you closed the store 2 months ago, just let me know and I can provide that info for you.
If there is anything else I can help you with, please let me know, I'm happy to help!