Post Baby Tum!

I am currently trying to loose weight but my biggest thing I want to sort is my tummy!
Over 4 years ago I had a daughter who was born my emergency c-section. When I was pregnant I ate what I wanted, so I put on quite a bit of weight!

I do sit ups using an exercise ball, and regularly use my stepper at home. I am eating 1200 calories a day to help loose weight.
I have noticed when I loose weight it comes off everywhere apart from my tummy!

Any suggestions on good exercises to help loose my tum and tone it up? Help!