Updating partial view in partial view using MVC Ajax

I have an MVC 5 web application that contains a Razor View called CreateProposal and it accepts a ViewModel called ProposalViewModel. This view includes a reference to a partial view called _Proposal , which also accepts a ViewModel.

View CreateProposal

@model STAR.UI.ViewModels.ProposalViewModel

<div class="row">
    @Html.Partial("_Proposal", Model)
</div>

      

        
        
        
      

    

Partial View _Program also references another partial view called _ExistingAttachments , which also accepts a ViewModel.

_Application of partial

@model STAR.UI.ViewModels.ProposalViewModel

<div class="col-md-6" id="proposalAttachments">
     @Html.Partial("_ExistingAttachments", Model)
</div>

      

        
        
        
      

    

_Changing Partial Attributes

@model STAR.UI.ViewModels.ProposalViewModel

<div class="form-group">
    <label>Existing Attachments</label><br />
    @Html.Hidden("hiddenAttachmentID", "", new { @id = "hiddenAttachmentID" })
    @if (Model.Attachments != null)
    {
        foreach (var upload in Model.Attachments)
        {
            <a href="~/Content/uploads/@upload.fileName">@upload.fileName</a>
            <a href="#" class="btn btn-danger btn-xs" data-toggle="modal" data-target="#ModalDeleteAttachment" data-id="@upload.fileID">Remove</a><br />
        }
    }
</div>

      

        
        
        
      

    

_ExistingAttachments Partial displays a list of href links and a Remove link next to them. After the user clicks the delete link on the element they want to delete, the id of that post is then stored in a hidden text box using a bit of jQuery.

JQuery

$(document).on('click', '.btn.btn-danger', function () {
        var id = $(this).data('id');
        //alert(id);
        $('#hiddenAttachmentID').val(id);

    });

      

        
        
        
      

    

The user is then presented with a modal confirm checkbox and after confirming the deletion, an Ajax call is made, which should then update the Partial _ExistingAttachments inside the Partial _Proposal

$.ajax({
        type: "GET",
        url: '/Proposal/DeleteAttachment/',
        data: { id: $("#hiddenAttachmentID").val() },
        error: function () {
            alert("An error occurred.");
        },
        success: function (data) {
            alert("Worked.");
            $("#proposalAttachments").html(data);
        }

});

      

        
        
        
      

    

MVC controller

public ActionResult DeleteAttachment(int id)
{
    //Delete entry using passed in id
    ProposalViewModel model = new ProposalViewModel();
    //Code to populate ViewModel
    return PartialView("_ExistingAttachments", model);
}

      

        
        
        
      

    

Everything works well until I update the Partial View _ExistingAttachments , but it doesn't.

Sorry for the long question, but hopefully can spot what I'm doing wrong.

Please, help.

UPDATE

I must add, the code turns it into an Ajax Success function and alert ("Worked"); called. However, instead of Partial Refresh, my Edit action within the same controller is called

[HttpPost]
public ActionResult EditProposal(ProposalViewModel model)