Hello, thank you for your reply of [date of the refusal]. You declined the refund for order [order number] because [reason the merchant gave].
That does not match what happened: [what went wrong in one sentence]. I have attached the order confirmation and [the document that answers the reason].
Please refund [amount] to my original payment method by [date you expect a decision]. If I do not hear back by then, I will ask my card issuer to review the charge.