@Lotte12 Go to your calendar and look to the right - you should see a box marked "Promotions." Click through that and see if there's something labeled "Active Promotions." If so, choose that and then select "Delete."
Although I believe the discount is in place because you said it is @Lotte12, normally you'd see some indication of a discount on the discounted dates. Where do you see it? When you preview your listing?