Unfortunately I don't speak Spanish, but given that while many people here speak English or even some German, Spanish speaking people are rare to find in The Netherlands, let me try to help you anyway, by replying to what Google Translate thinks you asked in English.

I assume the subscription you described is NS Flex Weekend Vrij. Given that it's only some pf your trips during weekends you are asked to pay for, I don't think there were any problems with the activation of your subscription. I'm afraid I don't expect your invoice is actually wrong either 'though. There are many things your subscription doesn't cover and without examples of things you've received an invoice for, I can only guess, but let me try anyway.

Might it be that you traveled with another company or at least (erroneously) checked in with them instead of NS? Or did you perhaps travel on the Intercity Direct between Schiphol Airport and Rotterdam Centraal? Or did you maybe pay for something other than a train with your card, e.g. did you rent a bike? Those costs are not covered by your subscription.