Dropbox file uploading not showing 409 error

I'm uploading file using Dropbox core API. I have written the upload code like-

RequestResult strReq = OAuthUtility.Put
                            (
                            "https://api-content.dropbox.com/1/files_put/auto/",
                            new HttpParameterCollection
                        {
                            {"access_token", "Token"},
                            {"path","/file.txt"},
                            {"overwrite", "false"}, 
                            {"autorename","false"}, 
                            {stream}
                        }
                            );
Suppose there is a existing file in root folder 
named file.txt and I'm again trying to upload 
the same name file to same folder.
I have written overwrite= false 
and autorename=false but surprisingly there 
is no error status code returning 
in the response.Always returning 
the success code 200 in the response.
I need to show the proper error code.