Doubt about Spring + Jquery

Alright? I've just started the Jquery + Spring MVC study. I'm developing an application where a person populates a phone field and through the pre-set a combo will be populated with the state and all cities of this state for the user to select. Here is my code example:

HTML

<div class="div-estado col-sm-3 ">
<input type="text" class="form-control row nomeEstado" id="estado" th:field="*{estado}" name="estado" readonly="readonly">
</input>
</div>

SCRIPT

$('.js-telefone').change(function(){
    var numTelefone = $('.js-telefone').val();
    var preFixo = numTelefone[1]+numTelefone[2];
    var urlRequisicao = '/sistemas/todasCidades';
    var response = $.ajax({
        url: urlRequisicao,
        type:'PUT',
        data:{
            numPreFixo:preFixo              
        }
    });

CONTROLLER

@RequestMapping(value ="/todasCidades", method=RequestMethod.PUT)
public @ResponseBody String listaTodasCidades(@ModelAttribute String numPreFixo ) {
    System.out.println("Prefixo:"+numPreFixo);
    return "ok";
}

The request is being submitted I can see through the Chrome developer tools, but I am not able to access the number being sent, System.out.println is printing null. can anybody help me?