custom select2 directive, ng-model update not happening in angularjs

Question

Using jquery-select2 (not ui-select) and angular, I'm trying to set the value to the ng-model.
I've tried using $watch and ng-change, but none seem to fire after selecting an item with select2. I have even tried with directive but unable to get model binding value using angular latest version form 1.6 and above 1.7x. plunker:sample code

<div class="col-md-6 service">
  <select select2 class="form-control" name="service" id="service"
          ng-model="selected" style="width: 200px;" required>
    <option value="">--Select--</option>
  </select></div>

Any advice would be greatly appreciated! :)

---

app.directive('select2', function() {
  return {
      restrict: 'A',
      require: 'ngModel',
      link: function(scope, element, attr, ngModel) {

        scope.dependentVals = {
                party: ["service", "inputformat", "psa"],
                service: ["inputformat", "psa"],
                inputformat: ["psa"]
            }

          //$this becomes element
          debugger
          element.select2({

              //options removed for clarity

              //    var pageLimitCount = 500, add_method = 'GET';
            // $(".select2Dropdown").each(function () {

            //  $(this).select2({
                    ajax: {
                        url: 'data.json',
                        type: 'GET',
                        dataType: 'json',
                        delay: 250,
                        crossDomain: true,
                        processResults: function (data) {
                          debugger;
                            var myarr = []
                            for (var j in data) {
                                myarr.push({
                                    'id': data[j].actualvalue,
                                    'text': data[j].displayvalue
                                })
                            }
                            return {
                                results: myarr,
                                pagination: {
                                    more: data.length >= 500
                                }
                            };

                        },
                        cache: true

                    },
                    placeholder: 'Select',
                    minimumInputLength: 0,
                    allowClear: true,
                    dropdownParent: $('.'+element.attr('name'))
                });

                element.on("select2:unselect", function (e) {

                    $('#uploadHere').css({
                        "pointer-events": "none",
                        "opacity": 0.5
                    });

                    for (var i in scope.dependentVals[element.attr('name')]) {
                        $("[name=" + scope.dependentVals[element.attr('name')][i] + "]").val("").trigger("change")
                    }
                });

                element.on("select2:select", function (e) {

                    $('#uploadBtn').val('')
                    $('#uploadHere').css({
                        "pointer-events": "none",
                        "opacity": 0.5
                    });

                    for (var i in scope.dependentVals[element.attr('name')]) {
                        $("[name=" + scope.dependentVals[element.attr('name')][i] + "]").val("").trigger("change")
                    }
                });
            // });
          // });

          element.on('change', function() {
               console.log('on change event');
               var val = element.value;
               scope.$apply(function(){
                   //will cause the ng-model to be updated.
                   ngModel.setViewValue(val);
               });
          });
          ngModel.$render = function() {
               //if this is called, the model was changed outside of select, and we need to set the value
              //not sure what the select2 api is, but something like:
              element.value = ngModel.$viewValue;
          }

      }
  }
});