Changing or cancelling train tickets is only possible if the Terms and conditions allow it.
Flexible fares do not have any or have less cancellation fees than non-flexible fares. Non-flexible fares cannot be cancelled.
The terms and conditions are explained for each ticket in My NSI.
If you have bought your ticket on NSInternational.com or via NS International Customer service, follow the step-by-step instructions on Change or cancel your trip to cancel your ticket yourself.
If you can exchange or cancel your ticket online, but instead ask NS International Customer service or a NS International Service desk to do this for you, you pay a service fee.
In all other cases, contact the original point of sale.