you can find answer here firebase.google.com/docs/cloud-messaging/…
Try to put title and message into notification object instead of data object

{
  "message":{
    "token":"..",
    "notification":{
      "title":"title",
      "body":"here your message"
    },
    "data" : {
      "custom_arg_1" : "custom_arg_1",
      "custom_arg_2" : "custom_arg_2"
    }
  }
}