How can I clean my walls?

Since some of the paint already came off the wall and you have the scuff marks, I recommend that you repaint the walls entirely in that room. This will likely be easier than touching up or cleaning the scuff marks. You can consider painting the room a different color or you can choose a color that is similar or the same as the original color if you like it.

If the spot where the paint came off is small and you still want to clean the scuff marks, I recommend that you test a mild detergent such a dishwashing liquid and water on an inconspicuous test area to see if it will remove the flat paint. On some interior flat paints, the paint will come off when you try to clean the wall with any type of detergent or cleanser. If you can find a mild detergent that will remove the scuff marks but not remove the paint then you will be able to clean the marks without repainting the room.