Well a couple of questions.
1. do you manually move the ball with a set.xy at any point.
If you do I suggest examining these.
2. Is your ball only moving due to bullet instructiosn.
If yes. no worries it's a good step :)
3. Thicken you walls. At certain velocity the ball can move fast enough on the logic level to pass through part of a thin wall.
Thicken the wall. If you need to hide the thick wall then put an image to hide the thicker wall.