The pricing scheme is a bit odd.
It starts with a data plan: 30GB is $225, although they sometimes run "double your data" sales that lets you sign up for 15GB ($100) and get 30GB. You then add "device charges" that give you unlimited calling and text. The first one is $40. I think that the second is, too, but that they 3rd and beyond get cheaper. Finally, you get a "discount" for NOT being under a contract. That discount is $15/month if you have a data plan that's less than 10GB or $25/mo for 10GB and higher. So, for you right now, $225 + $40 - $25 = $240.
Moral: look for a sale or stay on a grandfathered unlimited plan if you can.