Сообщения чата не загружаются должным образом

Я попытался создать систему сообщений чата, но старые сообщения, кажется, все еще остаются, когда вызываются новые сообщения.

Кто-нибудь может помочь? Кроме того, иногда, когда создается новый пользователь, и он общается с другим пользователем, сообщения от другого пользователя не отражаются в чате нового пользователя.

override func viewWillAppear(_ animated: Bool) {
            super.viewWillAppear(animated)
            navigationItem.title = "Chat"
            DispatchQueue.global(qos:.userInteractive).async {
                DispatchQueue.main.async {
                    self.loadPosts()
                    self.loadPostsReceivedMessage()
                }
            }
        }

    //Get Message sent
       func loadPosts() {
            let senderIDNumber = Auth.auth().currentUser?.uid
            let chatsRef = db.collection("chats").order(by: "timestamp", descending: false)
            chatsRef.whereField("senderID", isEqualTo: senderIDNumber!).whereField("receiverID", isEqualTo: receiverIDNumber)
                .addSnapshotListener { querySnapshot, error in
                    guard let documents = querySnapshot?.documents else {
                        print("Error fetching documents: \(error!)")
                        return
                    }
                    for document in documents {
                        let messageText = document.data()["message"] as? String
                        let senderIDNumber = document.data()["senderID"] as? String
                        let receiverIDNumber = document.data()["receiverID"] as? String
                        let timestamp = document.data()["timestamp"] as? String
                        guard let sender = document.data()["sender"] as? String else {return}
                       // let conversationsCounter = document.data()["conversationsCounter"] as? Int
                        guard let profileUrl = document.data()["profileUrl"] as? String else { return}
                        let chat = Chat(messageTextString: messageText!, senderIDNumber: senderIDNumber!, receiverIDNumber: receiverIDNumber!, timeStampString: timestamp!, profileImageUrl: profileUrl, senderString: sender)
        self.chats.append(chat)
        print(self.chats)
        self.collectionView.reloadData()
        }
        }
        }


        //Get message received
        func loadPostsReceivedMessage() {
           /* let uid = Auth.auth().currentUser?.uid
            let ref = Database.database().reference()
            ref.child("users").child(uid!).observeSingleEvent(of: .value, with: { (snapshot) in
                if let dic = snapshot.value as? [String: AnyObject]{
                    let currentUser = dic["username"] as? String
                    let senderIDNumber = Auth.auth().currentUser?.uid
                } */
                    let chatsRef = db.collection("chats").order(by: "timestamp", descending: false)
                    print("thecurrentreceiver"+senderString)
                    print("thecurrentsender"+receiverIDNumber)
            chatsRef.whereField("receiverID", isEqualTo: senderString).whereField("sender", isEqualTo: receiverIDNumber)
                        .addSnapshotListener { querySnapshot, error in
                            guard let documents = querySnapshot?.documents else {
                                print("Error fetching documents: \(error!)")
                                return
                            }
                            for document in documents {
                                let messageText = document.data()["message"] as? String
                                let senderIDNumber = document.data()["senderID"] as? String
                                let receiverIDNumber = document.data()["receiverID"] as? String
                                let timestamp = document.data()["timestamp"] as? String
                                // let conversationsCounter = document.data()["conversationsCounter"] as? Int
                                guard let profileUrl = document.data()["profileUrl"] as? String else { return}
                                guard let sender = document.data()["sender"] as? String else {return}
                                let chat = Chat(messageTextString: messageText!, senderIDNumber: senderIDNumber!, receiverIDNumber: receiverIDNumber!, timeStampString: timestamp!,profileImageUrl: profileUrl, senderString: sender)
                                print("whatisthemessage"+messageText!)
                                self.chats.append(chat)
                                print(self.chats)
                                self.chats.sort{$0.timestamp < $1.timestamp}
                                self.collectionView.reloadData()
                            }
                    }
        }