Has anyone tried cancelling an award through the website? How does this work?

For example if I have a C-class award that I paid 29 euro taxes on. Would I then be asked to pay 21 euro when cancelling since there is a 50 euro cancellation fee? Does that even work through the website, or would I have to call in?

I'm thinking to book an award as a backup flight. This means however that I won't be able to cancel until I'm sure to have made my connection and that I won't need the backup. But at that time I likely won't have time to call in to the PSL to ask for a cancellation of the backup flight. If its a few clicks on the website I can probably do that though..