Your second screenshot seems to indicate that you are still travelling on credit. That should not be the case if you have an NS Flex season ticket; then you will receive an invoice for all costs incurred at the end of the month.

That you needed to load credit is an indication that your season ticket is not active yet. After you buy a season ticket you need to activate it at a ticket machine. Until you do so, the season ticket will not be operational. You should have received an email with instructions on this.

I would advise you to activate the subscription as soon as possible and contact customer service directly to see if you can be refunded for the extra costs you made. That 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. Note that it can take a few days to get a reply via social media.