Beste antwoord door Momo
Do you have NS Flex without NS subscription and used bus, tram of metro?
The first thing you need to is find out what the invoice is for, either by checking your invoice in your MijnNS account or contacting the customer service. Since it is very busy at the various channels for customer service checking MijnNS is faster.
If there is no invoice or the invoice is not correct then you can contact customer service to explain and/or ask for a refund.