Request a Refund for wrong check out

I would like to request a refund for a wrong check out with my ov chipkaart when I should have used my international train ticket. NS will take 24 euros of my account from this. How can I request this refund and submit the proofs since it is a non ordinary refund request? Please note that I cannot in my account see any link to request this refund. Would be great if you can send me the form for me to fill in and tell me where this and the proof documentation should be sent to. Thank you!