Save data from a JComboBox in the Access database

I made a Form that is what I will save in one of the Access tables and one of the data I use with JComboBox and when doing a desktop test (run to test) it does not let me save the data (items) of the JComboBox.

The Database I do in Access is for a project, in the future I will use SQL and modify this project so that it works in SQL.

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private void RegistrarActionPerformed(java.awt.event.ActionEvent evt) {                                          
   if (tipo=="n") {
            try{
                Statement st = cn.createStatement();
                String sql = "insert into Clientes(Cuit, Nombre, Telefono, Direccion, Ciudad_Id, Situacion Frente IVA, Email)"
                +"values('"+this.Cuit.getText()+"','"+this.Nombre.getText()+"','"+this.Telefono.getText()+"','"+this.Direccion.getText()+"','"+this.Ciudad.getText()+",'"+this.IVA.getSelectedItem()+"','"+this.Email.getText()+"')";
                st.executeUpdate(sql);
            }catch (Exception e){
                System.out.print(e.getMessage());
            }
        }
        else{
            try{
                Statement st = cn.createStatement();
                String sql = ("UPDATE Clientes SET Cuit='"+Cuit.getText()+"'Nombre='"+Nombre.getText()+"',Telefono='"+Nombre.getText()+"',Direccion='"+Direccion.getText()+"',Ciudad='"+Ciudad.getText()+"', Situacion Frente IVA='"+this.IVA.getSelectedItem()+"','"+this.Email.getText()+"'  WHERE Id='"+id.getText()+"',");
                st.executeUpdate(sql);
            }catch (SQLException e){
                System.out.print(e.getMessage());
                JOptionPane.showConfirmDialog(null,"Error");
            }
        }
        this.Nombre.setEnabled(false);
        this.Cuit.setEnabled(false);
        this.Direccion.setEnabled(false);
        this.Ciudad.setEnabled(false);
        this.Telefono.setEnabled(false);
        this.IVA.setEnabled(false);
        this.Email.setEnabled(false);
        this.id.setText("");
        this.Nombre.setText("");
        this.Cuit.setText("");
        this.Direccion.setText("");
        this.Ciudad.setText("");
        this.Telefono.setText("");
        this.Email.setText("");
        cargagrilla("");
        Registrar.setEnabled(false);
        Nuevo.setEnabled(true);
        this.Modificar.setEnabled(true);
        Eliminar.setEnabled(true);
    }                            

'

MODIFY BUTTON (TO MODIFY THE DATA THAT IS SAVED IN THE DATABASE AND SHOWN IN JTable)

private void ModificarActionPerformed(java.awt.event.ActionEvent evt) {                                          
    int fila=datos.getSelectedRow();
    if (fila>=0){
        tipo="m";
        id.setText(datos.getValueAt(fila,0).toString());
        Cuit.setText(datos.getValueAt(fila,1).toString());
        Nombre.setText(datos.getValueAt(fila,2).toString());
        Telefono.setText(datos.getValueAt(fila,3).toString());
        Direccion.setText(datos.getValueAt(fila,4).toString());
        Ciudad.setText(datos.getValueAt(fila,5).toString());
        IVA.setSelectedItem(datos.getValueAt(fila, 6).toString());
        Email.setText(datos.getValueAt(fila, 7).toString());
        Nuevo.setEnabled(false);
        id.setEnabled(false);
        Nombre.setEnabled(false);
        Ciudad.setEnabled(false);
        IVA.setEnabled(false);
        Cuit.setEnabled(false);
        Registrar.setEnabled(true);
        Telefono.setEnabled(true);
        Direccion.setEnabled(true);
    }
    else{
        JOptionPane.showConfirmDialog(null, "no selecciono fila");
    }
    Direccion.setEnabled(true);
    Telefono.setEnabled(true);
    Registrar.setEnabled(true);
}