How to *really* delete WhatsApp images that were already deleted?

I've deleted around 800 images from the WhatsApp folder using Google's Photos app, but the problem is that no space was freed at all. I'm guessing those images are still available at /sdcard/WhatsApp/Media/WhatsApp Images. Is there a way to delete those 800 *"original photos"* without having to manually select them again? I'm using Motorola Moto X Play, Android 6.0.1, no SD card at all. PS: I have Google Photos backup disabled even before that event.