Insistent ongoing notification not working on Android

Question

I have been trying to create an incoming call type notification for my Android app, written in native Java code, and in many resources online I have read that using the .setOngoing(true) tag on the NotificationBuilder would be enough to have the desired behaviour of the notification being visible, playing the ringtone sound until it is clicked, but that has not worked for me. I have also tried using the flags Notification.FLAG_INSISTENT and Notification.FLAG_NO_CLEAR without success.

Here is my current code:

private void ringtone(Context context){
        String channelId = "call_channel";

        Intent notificationIntent = new Intent(context, MainActivity.class);
        PendingIntent contentIntent = PendingIntent.getActivity(context, 0, notificationIntent, PendingIntent.FLAG_IMMUTABLE);
        
        Uri ringtoneUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_RINGTONE);
        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, channelId)
                .setSmallIcon(R.drawable.ic_launcher_background)
                .setContentTitle("Incoming Call")
                .setContentText("You have an incoming call")
                .setCategory(Notification.CATEGORY_CALL)
                .setOngoing(true)
                .setAutoCancel(true)
                .setPriority(NotificationCompat.PRIORITY_MAX)
                .setContentIntent(contentIntent);
        
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

            NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
            CharSequence channelName = "Incoming Calls";
            int importance = NotificationManager.IMPORTANCE_HIGH;

            NotificationChannel notificationChannel = new NotificationChannel(channelId, channelName, importance);
            notificationChannel.enableVibration(true);
            long[] pattern = {0, 1000, 500, 1000};
            notificationChannel.setVibrationPattern(pattern);
            AudioAttributes att = new AudioAttributes.Builder()
                    .setUsage(AudioAttributes.USAGE_NOTIFICATION_RINGTONE)
                    .setLegacyStreamType(AudioManager.STREAM_RING)
                    .setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)
                    .build();
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
                notificationChannel.setAllowBubbles(true);
            }
            notificationChannel.setLockscreenVisibility(NotificationCompat.VISIBILITY_PUBLIC);
            notificationChannel.setSound(ringtoneUri,att);
            notificationManager.createNotificationChannel(notificationChannel);
        }else{
            notificationBuilder.setSound(ringtoneUri);
        }

        Notification notification = notificationBuilder.build();
        notification.flags |= Notification.FLAG_INSISTENT | Notification.FLAG_NO_CLEAR;

        NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(0, notification);

    }

My intention is to have an incoming call type of notification much like other applications such as MS Teams, Whatsapp, ETC. and my issue is that the notification gets minimized after showing on screen for a few seconds, and the ringtone stops shortly after. Thank you for any help with this.