Как удалить сообщения из базы данных firebase?

Я создаю приложение для чата. Я хочу, чтобы пользователи могли удалять чаты и сообщения из базы данных firebase. Ниже приведен код адаптера сообщений, который я пытался использовать для удаления сообщений, он отлично работает, когда я долго нажимаю на сообщение, но когда я снова вхожу в приложение, сообщения возвращаются. Я использую базу данных firebase

package com.paddi.paddi.paddi;

import android.graphics.Color;
import android.support.v7.widget.RecyclerView;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.squareup.picasso.Picasso;

import java.util.List;

import de.hdodenhof.circleimageview.CircleImageView;

/**
 * Created by paddi on 15/11/2017.
 */

public class MessageAdapter extends RecyclerView.Adapter<MessageAdapter.MessageViewHolder>
{
    private List<Messages> userMessagesList;

    private FirebaseAuth mAuth;
    private DatabaseReference UsersDatabaseReference;







    public MessageAdapter(List<Messages> userMessagesList)
    {
        this.userMessagesList = userMessagesList;

    }


// I tried using this to delete the chats it works but every time i log into the app again the messages re-appear


    public void delete(int position){


        userMessagesList.remove(position);
        notifyItemRemoved(position);





    }




    @Override
    public MessageViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
    {

        View V = LayoutInflater.from(parent.getContext())
                                .inflate(R.layout.messages_layout_of_users, parent, false);


        mAuth = FirebaseAuth.getInstance();




        return new MessageViewHolder(V);



    }





    @Override
    public void onBindViewHolder(final MessageViewHolder holder, int position)
    {


        String message_sender_id = mAuth.getCurrentUser().getUid();
            Messages messages = userMessagesList.get(position);

        String fromUserId = messages.getFrom();
        String fromMessageType = messages.getType();

        UsersDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(fromUserId);
        UsersDatabaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                String userName = dataSnapshot.child("user_name").getValue().toString();
                String userImage = dataSnapshot.child("user_thumb_image").getValue().toString();

                Picasso.with(holder.ReceiverProfileImage.getContext()).load(userImage)
                        .fit().centerInside().placeholder(R.drawable.default_profile).into(holder.ReceiverProfileImage);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });


        if (fromMessageType.equals("text"))
        {
            holder.ReceiverMessageText.setVisibility(View.INVISIBLE);
            holder.messagePicture.setVisibility(View.INVISIBLE);
            holder.ReceiverProfileImage.setVisibility(View.INVISIBLE);
            holder.SenderMessageText.setVisibility(View.INVISIBLE);
            // You comment this last line out in case of any errors

            if (fromUserId.equals(message_sender_id))
            {
                // You comment this first line out in case of any errors
                holder.SenderMessageText.setVisibility(View.VISIBLE);
                holder.SenderMessageText.setBackgroundResource(R.drawable.sender_message_text_background);
                holder.SenderMessageText.setTextColor(Color.WHITE);
                holder.SenderMessageText.setGravity(Gravity.START);
                holder.SenderMessageText.setText(messages.getMessage());
            }

            else
            {

                holder.SenderMessageText.setVisibility(View.INVISIBLE);

                holder.ReceiverMessageText.setVisibility(View.VISIBLE);
                holder.ReceiverProfileImage.setVisibility(View.VISIBLE);
                holder.messagePicture.setVisibility(View.VISIBLE);

                holder.ReceiverMessageText.setBackgroundResource(R.drawable.receiver_message_text_background);
                holder.ReceiverMessageText.setTextColor(Color.WHITE);
                holder.ReceiverMessageText.setGravity(Gravity.START);
                holder.ReceiverMessageText.setText(messages.getMessage());
            }

           // holder.messageText.setText(messages.getMessage());
        }


    else
    {
          //  holder.messageText.setVisibility(View.INVISIBLE);
           // holder.messageText.setPadding(0,0,0,0);

//            holder.messagePicture.setForegroundGravity(22);
        Picasso.with(holder.ReceiverProfileImage.getContext()).load(messages.getMessage())
                .placeholder(R.drawable.default_profile).into(holder.messagePicture);
    }



}



@Override
public int getItemCount()
{
    return userMessagesList.size();
}


public class MessageViewHolder extends RecyclerView.ViewHolder implements View.OnLongClickListener
{
    public TextView SenderMessageText, ReceiverMessageText;
    public CircleImageView ReceiverProfileImage;
    public ImageView messagePicture;



    public MessageViewHolder(View view) {
        super(view);

        SenderMessageText = (TextView) itemView.findViewById(R.id.sender_message_text);
        ReceiverMessageText = (TextView) itemView.findViewById(R.id.receiver_message_text);
        messagePicture = (ImageView) view.findViewById(R.id.message_image_view);
        ReceiverProfileImage = (CircleImageView) view.findViewById(R.id.messages_profile_image);



        SenderMessageText.setOnLongClickListener(this);
        ReceiverMessageText.setOnLongClickListener(this);
        messagePicture.setOnLongClickListener(this);

    }


    @Override
    public boolean onLongClick(View v) {
        delete(getAdapterPosition());
        return true;

    }
}

}

Это снимок экрана моей базы данных для дерева сообщений: