Well if it is Fontana Syrup like it shows on the Starbucks site then it is 5 cal 2 carbs.
http://www.starbucksfs.com/Products/...ype=Sugar-Free
Now this is for 1 fl oz... perhaps they do not use that much?? 1 oz is about 2 tablespoons so I can see that much if not more being used
Maybe call back to the store and ask what brand of syrup they use and how many tablespoons?? I think they have the nutritional info on the back of the syrup pumps..