Android DownloadManager API not working with mobile Network


I use DownloadManager to download a zipped file from a PHP server.

If I use the WIFI network, everything works well (do not download if there is no internet connection).

But if I activate the mobile network of my phone, without having an Internet connection, the download starts and DownloadManager notifies me immediately that the download is completed.

If I look in the destination folder, I can not find anything.
For all that it works well if I have an internet connection (mobile).

Here is my code.
An idea ?

// method to get if phone is connected
private boolean isConnected() {
    ConnectivityManager connectivityManager = (ConnectivityManager) getContext().getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
    return networkInfo != null && networkInfo.isConnected();

//request to DownloadManager
DownloadManager.Request request = new DownloadManager.Request(uri_complete);
            request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_MOBILE |
                    Environment.DIRECTORY_MUSIC + "/audios", diminutif + ".zip");
downloadId = downloadManager.enqueue(request);

// My PHP file  
 \<?php $path = 'audios'; $file\_name = $\_GET['file']; if(isset($file\_name)) { $fichier = $path . '/' . $file\_name . '.zip'; //if(file\_exists($fichier)) { header('Content-Description: File Transfer'); header('Content-Type: application/octet-stream'); header('Content-Disposition: attachment; filename='.basename($fichier)); header("Content-Transfer-Encoding: binary"); header('Expires: 0'); header('Cache-Control: must-revalidate'); header('Pragma: public'); header('Content-Length: '.filesize($fichier)); ob\_clean(); flush(); readfile($fichier); exit; } ?\>