The “40% korting in het weekend”, if it is mentioned below Treinreizen, is what you have to pay for journeys you made during weekends with a season ticket that entitles you to discount during the weekends.
Correctiontarieven, or in English: correction fees, are amounts you have to pay if you did something wrong, e.g. forgetting to check in or out. See this page. This might happen by accident if you check in or out at a pole or gate of the wrong transport company, e.g. Arriva instead of NS. You can go through your travel history to see if this happened.
In any case, if you feel your invoice is incorrect, then you should contact customer service directly to have this corrected. Usually, this is most easily done by phone, as they are available 24/7 at 030-751 51 55. You may also contact them by chat (click the link Chat with NS on this page) or by sending a message on Twitter or Facebook.