Hyde here from Shopify.
When it comes to app refunds we first need the app developers to approve the refunds, as your agreement is with them - we're simply the middleman for billing.
So I would recommend reaching out to them to ask for that refund (you can contact them here) and explaining the situation to them. There's also a LiveChat option here.
If they approve it they will reach out to us to process that and we will do it for you!
All the best, Hyde.