Javascript not working eptialy preent default

see below my code e.prevnt default not working the form got submited :

this is the modal its working without any probleme the only issue is preventing submition
so I need your help please take a look at this and let me know

   <div id="Edit-ROT" class="modal fade" tabindex="0" role="dialog" aria-labelledby="add-contactLabel" aria-hidden="true">
                        <div class="modal-dialog">
                <div class="modal-content">
                
                
                    <div class="modal-header">
                        <h5 class="modal-title" id="add-contactLabel">Modifier Recommandation OT</h5>
                        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
                    </div>
                    <div class="modal-body">
                    <div class="statusMsg"></div>
                    <div class="alert alert-success alert-dismissible" id="success" style="display:none;">
              <a href="#" class="close" data-dismiss="alert" aria-label="close">×</a>
            </div>
               
                          
            <form id="ModifierROT" action="" method="post" >
                            
                        
                          
                                          
                                              
                                     <input type='hidden' name='ajouter' value='modifier_rot'/>
                      <input type='hidden' name='ideditROT' id='ideditROT' value=''/>
                            
                        
                     
                    
                    <div class="modal-footer">
                        <button type="button" class="btn btn-default " data-dismiss="modal">Cancel</button>
                        <input type="submit" class="btn btn-primary "  id='submitbtn' name="ajouter_caution" value="Enregistrer">
                    </div>
                       </form>
            
                </div><!-- /.modal-content -->
            </div><!-- /.modal-dialog -->
        </div><!-- /.modal -->
        </div><!-- /.modal -->
            </div><!-- /.modal -->

this is the JS its working without any probleme the only issue is preventing submition
so I need your help please take a look at this and let me know if you require any further help

        // Modifier ROT


   $("#Modifierrot").on('submit', function(e){
        e.preventDefault();
        $.ajax({
            type: 'POST',
            url: 'caution/nouvelle_caution.php',
            data: new FormData(this),
            dataType: 'json',
            contentType: false,
            cache: false,
            processData:false,
            beforeSend: function(){
                $('.submitBtn').attr("disabled","disabled");
                $('#Modifierrot').css("opacity",".5");
            },
            success: function(response){
                $('.statusMsg').html('');
                if(response.status == 1){
                    $('#Modifierrot')[0].reset();
                    
             $('.statusMsg').html('<p class="alert alert-success">'+response.message+'</p>').delay(5000).fadeOut('slow');
                    
                }else{
                    $('.statusMsg').html('<p class="alert alert-danger">'+response.message+'</p>');
                }
                $('#Modifierrot').css("opacity","");
                $(".submitBtn").removeAttr("disabled");
            
             },
    error : function(request, status, error) {

        var val = request.responseText;
        alert("error"+val);
    }
        });
    });