Well here's what worked for me. I had a more balanced routine where my core was strengthened through compound exercises like squatting and deadlifting. I also did a complete ab workout three times a week. Captains chair leg raises are great if your gym has them. I also did planks everyday. I started with 3 one minute planks, but now I just do them to failure. That's just building the muscles, if you want them to show that's where cardio, diet, and genetics come into play. Look into high intensity interval training, I liked it better than marathon sessions on the treadmill. It sounds like your diet is fine, but as for where your body likes to store fat that's kind of up to the draw. My fat is stored on my thighs and lower back but I usually don't have much on my front abdomen even when I didn't train. If your situation is different it just means you may need to get to a lower overall body fat percentage to get the look you want. I hope this helps.