I'm not sure what you mean by "registered account”.

Do you have an NS Flex subscription? In that case, the invoice should be paid automatically by direct debit, from the bank account that is linked to your subscription.

If the direct debit did not work for some reason NS will send an e-mail with payment instructions, to make a transfer to the bank account of NS; this e-mail will mention the IBAN and the payment communication to use.

It is best to contact customer service. They are open between 07:00 and 23:00 (Dutch time). Customer service can be reached by telephone, chat, Facebook and Twitter.