Customer servive should be able to correct this for you so I'm afraid you'll have to try contacting them again.

What you should have done and should do if you ever arrive on a Dutch station with a different ticket than an ov chipcard, is use the ticket you actually traveled on to exit the station. There should be a code printed on it you can use to open the gates.

And if that ticket doesn’t work to open a gate you can ask for assistance by pressing the blue button on one of the assistance and alarm machines near the gates. They will open the gate for you remotely.

Never ever use another card to open gates if you have a valid ticket for your journey. 

If you were billed €12 it means you have NS Flex and checked out with a missing check-in.

NS Customer Service must correct that for you (3 times per year).

Also tell them your international (Thalys) ticket didn’t work. That way, the missing check-in might not count towards those 3 times per year.

Thanks all for your reply, I contacted them through Facebook and they were much helpful than on the phone and they took the Thalys ticket and make a refund for me