You can correct this yourself and ask for a refund at uitcheckgemist.nl.

Which signs did you follow? Blue ones with white text or white ones with black text?

Finding the exit shouldn't be that hard as there are only two options. It looks like to that instead of following the exit signs, you've taken the stairs to the metro and then exited the metro station. By doing so, you checked out at RET instead of NS. Check via uitcheckgemist.nl if anything was charged by RET. The NS part can be corrected via My NS or a call to customer service.

How did you get at the metro while you have to go through the train gates first before you can even get to the metro?

He got at the tram stop, which is where two exits from the metro station are. In one direction at Rotterdam Blaak, there are tranfer poles on the platform next to the stairs and you don't pass through gates to reach the metro station.

Ah, sorry misunderstood it then…

Thought it was about Rotterdam Central .

I am new to Rotterdam and didn’t know this . 

It's okay you can just do what Tochjo recommended.

You always have to check out at a pole or gate of the same company where you checked in. It's not that complicated.

Thank you so much for your support. 

For a complete overview of all check-ins and check-outs, create an account at ov-chipkaart.nl and connect your OV-chipkaart to it.

If you have an anonymous OV-chipkaart (no name, no photo), then you do not need an account.

If you (topic starter) checked in en out using a debit card or credit card, you should go to ovpay.nl and use the NLOV-number on your bank statement to get info and maybe fix things.