As long as you post the outgoing and returned funds to the same nominal code it won’t matter too much. One option would be to create a new nominal code (under assets/liabilities) called something like “Chargebacks” or “Fraud” and post both entries there.
You don’t even need to create any invoices, just tag from the bank as “Something else not on the list” and post directly to the nominal code.
Hope that helps!