The trains between Zwolle and Heino(-Enschede) are not operated by NS, but by Keolis, under the name of Blauwnet. This means you need to check in at a Blauwnet gate in Zwolle, not an NS gate. It sounds like you might have made a mistake there, since the situation you describe could occur if you checked in at an NS gate. At Heino there are only Blauwnet poles, so you cannot check out with NS there.

To sum up, it sounds like you have checked in at NS and checked in again at Blauwnet in Heino, now having missed check-outs with both companies. (The missing Blauwnet checkout won't show up in the NS app travel history if you’re travelling on credit.)

To have this corrected, you could check if you can fix this yourself at the website uitcheckgemist.nl.

If you can't, or it's not clear to you what to do exactly, just contact NS customer service directly. They can surely help you correct the erroneous NS check-in. Usually, this is most easily done by phone, as they are available 24/7 at 030-751 51 55. You may also try to contact them by chat (click the link Chat with NS on this page) or by sending a message on Twitter or Facebook.

Then you need to contact Keolis customer service to have the missing check-out with them settled. You can find their contact details at the bottom of this page (form, chat, Facebook or Twitter).

Hi!

I forgot to check-out on 29th march from Utrecht Station to Hilversum Sportpark. 
 

Is it possible to get fee back? 

Hello LEHTIMAKI. Welcome to the community.

You can apply for a refund here: www.uitcheckgemist.nl or, if you have NS Flex, correct the journey via Mijn NS or contact our Customer Service.