Forget to checkout

Hello,

I had a train travel from Groningen to Schipol airport in August. During our trip, something went wrong with our train and we changed to another one. When we arrived, I was not sure if I could check out or not. I asked one of the passengers and she told me it’s an exceptional situation and you should not check out. Today I realized that I was charged extra. So I tried to correct it, but I received an email indicating 

I would appreciate it if you could help me with refunding and correcting the checkout.

Best regards,