RadioButton changes checked when scrolling Listview

Good afternoon, I have a problem with RadioGroup in a listview. Next, when I mark a RadioButtom and use the scroll of my listview, the markup I made appears on another RadioButto and not on what I had selected.  Here is the code for my adapter:

class AdapterAmcPersonalizada extends BaseAdapter {

    private final List<AvaliacaoMensal> mensal;
    private final Activity act;

    private AvaliacaoMensal flag;


    public AdapterAmcPersonalizada(List<AvaliacaoMensal> mensal, Activity act) {
        this.mensal = mensal;
        this.act = act;


    }


    @Override
    public int getCount() {
        return mensal.size();
    }

    @Override
    public Object getItem(int position) {
        return mensal.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = act.getLayoutInflater().inflate(R.layout.activity_layout_lista_amc, parent, false);

        final AvaliacaoMensal mensalAmc = mensal.get(position);

        //pegando as referências das Views
        TextView potencial = (TextView) view.findViewById(R.id.potencialLetra);
        TextView questao = (TextView) view.findViewById(R.id.questao);
        TextView titulo = (TextView) view.findViewById(R.id.titulo);
        RadioButton simButton = (RadioButton) view.findViewById(R.id.sim);
        RadioButton naoButton = (RadioButton) view.findViewById(R.id.nao);
        RadioButton naButton = (RadioButton) view.findViewById(R.id.na);

        //populando as Views
        potencial.setText(String.valueOf(mensalAmc.getPotencial()));
        questao.setText(String.valueOf(mensalAmc.getQuestao()));
        titulo.setText(String.valueOf(mensalAmc.getTitulo()));

        RadioGroup radioGroupAmc = (RadioGroup) view.findViewById(R.id.radioGroupAmc);
        flag = mensal.get(position);
        radioGroupAmc.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {

                switch (checkedId) {
                    case sim:

                        flag.radioButtonValues[0] = true;
                        flag.radioButtonValues[1] = false;
                        flag.radioButtonValues[2] = false;;

                        // trata radioValor1
                        break;
                    case nao:
                        flag.radioButtonValues[0] = false;
                        flag.radioButtonValues[1] = true;
                        flag.radioButtonValues[2] = false;
                        // trata radioValor2
                        break;
                    case na:
                        flag.radioButtonValues[0] = false;
                        flag.radioButtonValues[1] = false;
                        flag.radioButtonValues[2] = true;
                        // trata radioValor3
                        break;
                }

            }

        });



     if( flag.radioButtonValues[0] == true )
        {
            simButton.setChecked(true);
            naoButton.setChecked(false);
            naButton.setChecked(false);
        } else {
            if(flag.radioButtonValues[1] == true ){
                naoButton.setChecked(true);
                simButton.setChecked(false);
                naButton.setChecked(false);
            } else {
                if(flag.radioButtonValues[2] == true ){
                    naButton.setChecked(true);
                    simButton.setChecked(false);
                    naoButton.setChecked(false);
                }else {
                    simButton.setChecked(false);
                    naoButton.setChecked(false);
                    naButton.setChecked(false);
                }
            }
        }

In the following snippet, I check the position that is in my listview (flag) and check the value that is within radioButtonValues[] .

   if( flag.radioButtonValues[0] == true )
        {
            simButton.setChecked(true);
            naoButton.setChecked(false);
            naButton.setChecked(false);
        } else {
            if(flag.radioButtonValues[1] == true ){
                naoButton.setChecked(true);
                simButton.setChecked(false);
                naButton.setChecked(false);
            } else {
                if(flag.radioButtonValues[2] == true ){
                    naButton.setChecked(true);
                    simButton.setChecked(false);
                    naoButton.setChecked(false);
                }else {
                    simButton.setChecked(false);
                    naoButton.setChecked(false);
                    naButton.setChecked(false);
                }
            }
        }

Rating Class Mental:

 class AvaliacaoMensal {
        private String questao;
        private char potencial;
        private String titulo;
       boolean[] radioButtonValues = new boolean[3];
//Gets e sets

But it is not working as expected because the dialing is going to another RadioGroup, can anyone help me?