Problem "Instance Member can’t be accessed using Static access." in a simple registration system

Question

I’m trying to create a registration system and for some reason I can’t access the "put" (add) method, located in the "users.Dart", on the screen where the entries are shown, the "cadastros.Dart".

The following error appears: 'Instance Member "put" can’t be accessed using Static access.'

cadastrals.Dart

import 'package:flutter/material.dart';
import 'package:projetofinal/components/usuario_tile.dart';
import 'package:provider/provider.dart';
import 'package:projetofinal/provider/users.dart';
import 'package:projetofinal/model/user.dart';

class cadastros extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final Users usuarios = Provider.of(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('Usuarios Cadastrados'),
        actions: <Widget>[
          IconButton(
              onPressed: () {
                Users.put(User(  /*ERRO OCORRE NESSA LINHA */
                  id: '',
                  nome: 'teste',
                  email: 's',
                  telefone: 'w',
                  pfp: '',
                ));
              },
              icon: Icon(Icons.add))
        ],
      ),
      body: ListView.builder(
        itemCount: usuarios.count,
        itemBuilder: (cxt, i) => UserTile(usuarios.byIndex(i)),
      ),
    );
  }
}

Dart users.

import 'package:flutter/cupertino.dart';
import 'dart:math';
import 'package:projetofinal/data/dummy_users.dart';
import 'package:projetofinal/model/user.dart';

class Users with ChangeNotifier {
  final Map<String, User> _items = {...DUMMY_USERS};

  List<User> get all {
    return [..._items.values];
  }

  int get count {
    return _items.length;
  }

  User byIndex(int i) {
    return _items.values.elementAt(i);
  }

  void put(User user) {
    if (user == null) {
      return;
    }

    if (user.id != null &&
        !user.id.trim().isEmpty &&
        _items.containsKey(user.id)) {
      _items.update(
        user.id,
        (_) => User(
          id: user.id,
          nome: user.nome,
          email: user.email,
          telefone: user.telefone,
          pfp: user.pfp,
        ),
      );
    } else {
      //adicionar
      final id = Random().nextDouble.toString();

      _items.putIfAbsent(
        id,
        () => User(
          id: id,
          nome: user.nome,
          email: user.email,
          telefone: user.telefone,
          pfp: user.pfp,
        ),
      );
      notifyListeners();
    }
  }

//remover

  void remove(User user) {
    if (user != null && user.id != null) {
      _items.remove(user.id);
      notifyListeners();
    }
  }
}