You are just one of the many victims of a system that even many Dutch makes surprises.

You did NOT clearly tell what kind of subscription you had, and 1 for just 3€/month does not exist-its either 2 (for weekend discount) or 5 (off-peak discount). DalVrij cost 106/month (free travel starting in all off-peak hours).

IF you held an old-style subscription, it does not finish with just cancelling it- you ALSO have to confirm that on a yellow NS-machine. IF you already had the new style FLEX then this is not needed anymore, provided you turn it into Basic. YOu can still do that-and check via mijnNS what is exactly on the card. It is self-evident to first always check account-before asking things noone else can look into.

If I1] applies, then you can call NS (good luck with that-will take long time to connect) and ask to completely destroy card registration-which means you cannot use it anymore in case you ever return to NL. It seems you also still hold a dutch bank-account?