InstanceID and Regid GCM

Question

as I read, the function gcm.register() is deprecated. and I may use InstanceID.getToken() instead...

I use it as described here but every time I run the app, I get new RegID (Instance ID)..

here how I registered :

        @Override
        protected String doInBackground(Object[] voids) {
            String msg = "";

            if (gcm == null) {
                gcm = GoogleCloudMessaging.getInstance(MyApp.getContext());
            }
            InstanceID instanceID = InstanceID.getInstance(context1);
            EntryActivity. regid = null;
            try {

                EntryActivity.regid = instanceID.getToken(ConstantsGCM.senderID_ProjectID, GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
                Log.d("REG---", "========================>>>- regid= " + EntryActivity.regid);

            } catch (IOException e) {
                e.printStackTrace();
            }

            if (EntryActivity.regid != null)
                try {
                    storeRegistrationId(context1, EntryActivity.regid);
                } catch (PackageManager.NameNotFoundException e) {
                    e.printStackTrace();
                }
            Log.d("REG---", "- " + msg + "regid= " + EntryActivity.regid);
            return msg;
        }

and then I sent "regid" to my server and save it to database, Until now everythig worked fine, but When I send a message to the server via GCM (gcm.send(...); ) and call the "from" field of the message (in the server side) I get a different regID, and every time I restart the app and send I get new regID (for each instace the regId changed).

How to use Instance ID as constant RegID, I read the documentations but did not undersatnd how!