Did you travel by checking in and out with your bank card? Then you can check your travel history on this page (you can select English at the right top corner of the page). The reference number should start with NLOV and be 18 characters long in total (including NLOV).

If this doesn't answer your question, please be more specific. Which trips did you make, where did you find the reference number, where are you trying to enter it, and so on.

Thank you for your reply.

I took a few trips in Amsterdam over the past few days and I think the payments were grouped together.

I checked my bank account and saw the reference number ( NLOVXX111XXXX1X like this).

I tried to enter it on “Check travel history” of OVpay Self service.

I asked NS online on Twitter.They told me to contact OVpay who can only be reached by phone. Unfortunately, I’m in Hong Kong and I can’t call them.

If you are sure you entered the right number, I'd fill out this form to contact them.

Now, the payments are pending at the bank. 

“You can head to ovpay.nl/reisoverzicht or the OVpay app and fill in this code as well as the amount that was debited. “ (found it on OVpay)

Is it means I have to wait for the settlement and get the other number?

Travel with a debit/credit card are grouped per day and will be debited the next day, but they are listed as pending because there is no bank traffic in the weekend.

In case you want to contact them from abroad, call +31 10 892 50 63 (7.00am - 5.00pm)

I encounter the same issue: the reference number of NLOV is only 15 characters.

I used this form to contact them days ago, but I receive no response. Is there any other client service? (International phone calls are expansive thus I would avoid it.)