ControllerObject.Add(ClassObj);
var jresp = JsonConvert.SerializeObject(ControllerObject, Formatting.Indented);
You are converting ControllerObject into JSON to return, and given you are using .Add on it I assume it is a List or some other collection, so when you convert it to JSON you get the square brackets, even if there is only one item in the list. If you only want to return that one item then return ClassObj rather than ControllerObject
var jresp = JsonConvert.SerializeObject(ClassObj, Formatting.Indented);
Or return the first item in ControllerObject
var jresp = JsonConvert.SerializeObject(ControllerObject[0], Formatting.Indented);