Convert JSON to XML .net

I want to convert from JSON to XML but the return keep showing in JSON. No Error or bug

protected string convertToJSONorXML(object convertThisObj, returnDataFormat returnFormat, bool jsonformatting = false)
        {
            string returnString = "";

            if (returnFormat == returnDataFormat.JsonFormat)
            {
                return JsonConvert.SerializeObject(convertThisObj,
                                                    (jsonformatting) ? Formatting.Indented : Formatting.None, 
                                                    new JsonSerializerSettings { NullValueHandling = (jsonformatting) ? NullValueHandling.Ignore : NullValueHandling.Include }
                                                   );
            }

            returnString = toXML(convertThisObj);
            return returnString;
        }