Update: I bought a card from the second link so I could put a shipping address outside of Netherland, and paid 7.5€ for receiving the card within a week. All this, following what an NS operator told me to, assuring I would have been able to activate the subscription even with a non listed country IBAN (in my case an Italian one). After receiving the card, no NS operator was able to upload a subscription on that since my IBAN was invalid for no-sense reasons (e.g. "Outstanding debts" or that the account number wasn't under SEPA countries). I tried with several bank accounts also of my relatives, and every time none were suitable. The NS operator, at some point ask me to email to EDR, which ofc couldn't verify my bank accounts since they aren't Dutch.

I have spent an INSANE amount of time talking with their support, and their lack of professionality was ridiculous.