Asp.net MVC 5 - View Posting Null Data to Controller

Question

I'm working on an application that uses a View Model to pass data to a view, however when I attempt to save changes the user makes to the data and post it back to the controller for processing and storing in a database, I'm getting null values for everything in my view model. I've tried various other questions on here and none of the answers I've found have been able to solve this issue. I think it has something to do with the my use of a ListBox to display some of the data, but I'm fairly new to ASP.net MVC 5 and am not quite sure what I need to be doing here.

Below is the code for my view model, the relevant sections from the controller, and the view.

View Model

public class OrganizationViewModel
{
    public Organization Organization { get; set; }
    public IEnumerable<SelectListItem> RelatedContacts { get; set; }
}

Sending Data from Controller to View

[HttpGet]
    public ActionResult Edit(Organization organization)
    {
        IEnumerable<SelectListItem> contactsList = GetContacts(organization);
        var viewModel = new OrganizationViewModel()
        {
            Organization = organization,
            RelatedContacts = contactsList
        };

        return View("Edit", viewModel);
    }

Receiving Data from View

[HttpPost]
    public ActionResult SaveOrganization(OrganizationViewModel organizationViewModel)
    {
        organizationViewModel.Organization.Id = (int)TempData["Id"];
        organizationViewModel.Organization.LastEdited = DateTime.Today;
        organizationViewModel.Organization.DateAdded = (DateTime)TempData["DateAdded"];
        TempData.Clear();
        if (ModelState.IsValid)
        {
            organizationRepository.SaveOrganization(organizationViewModel.Organization);
            return RedirectToAction("Index", "Organization");
        }

        IEnumerable<SelectListItem> contactsList = GetContacts(organizationViewModel.Organization);
        var viewModel = new OrganizationViewModel()
        {
            Organization = organizationViewModel.Organization,
            RelatedContacts = contactsList
        };
        return View("Edit", viewModel);
    }

The Edit View

<div class="panel">
<div class="panel-heading">
    <h3>Editing @(Model.Organization.Name)</h3>
</div>

@using (Html.BeginForm("SaveOrganization", "Organization", FormMethod.Post))
{
    <div class="panel-body">
        @Html.HiddenFor(m => Model.Organization.Name)
        <div class="row">
            <div class="col-md-3 form-group">
                <label>Organization Name</label>
                @Html.TextBox("Name", null, new { @class = "form-control" })
            </div>
            <div class="col-md-3 form-group">
                <label>Address</label>
                @Html.TextArea("Address", null, new { @class = "form-control" })
            </div>
        </div>
        <div class="row">
            <div class="col-md-3 form-group">
                <label>Related Contacts</label>
                @Html.ListBox("RelatedContacts", Model.RelatedContacts, new { @class = "form-control", size = 10 })
            </div>
            <div class="col-md-3 form-group">
                <label>Custom Fields</label>
                <br />
                <input type="button" value="Add New Field" class="btn btn-default" />
            </div>
        </div>
        <div class="row">
            <div class="col-md-12 form-group">
                <label>Notes</label>
                @Html.TextArea("Notes", null, 10, 500, new { @class = "form-control", @style = "width: 100%; max-width: 100%;" })
            </div>
        </div>
    </div>
    <div class="panel-footer">
        <input type="submit" value="Save" class="btn btn-primary" />
        @Html.ActionLink("Cancel and return to List", "CancelEditOrAdd", null, new { @class = "btn btn-default" })
    </div>
}

Answer 1

Answering my own question for anyone who stumbles across this and wants to see the exact changes I made based on @Stephen Muecke's comments.

Changed all the @html.something()s into @html.somethingfor()s for fixed the issue with not receiving postback data for the Organization in the View Model, and then I created a new property in the view model to correspond with the selected index in the ListBox, which now reads @Html.ListBoxFor(m => m.SelectedIndexes, Model.RelatedContacts, ...). I'm now getting all the proper postback data and can relate the selected index to the Organization's related contacts.

Edit: Also changed my View Model to contain the properties of my Organization class and not an actual Organization object itself as a property.