asp.net mvc - Jquery Ajax, return success/error from mvc.net controller

Question

I would like to control when to reply an error message and when a success message but I am always get the error message:

here is what I am trying to do:

 $.ajax({
                type: "POST",
                data: formData,
                url: "/Forms/GetJobData",
                dataType: 'json',
                contentType: false,
                processData: false,

                success: function (response) {                    
                   alert("success!") 
                },
                error: function (response) {
                   alert("error") // I'm always get this.
                }

            });

Controller:

         [HttpPost]
            public ActionResult GetJobData(Jobs jobData)
            {

              var mimeType = jobData.File.ContentType;
              var isFileSupported = AllowedMimeTypes(mimeType);

             if (!isFileSupported){        
                     //  Error
                    Response.StatusCode = (int)HttpStatusCode.BadRequest;
                    return Content("The attached file is not supported", MediaTypeNames.Text.Plain);    
             }
            else
              {
                    //  Success
                    Response.StatusCode = (int)HttpStatusCode.OK;
                    return Content("Message sent!", MediaTypeNames.Text.Plain);     

               }   

            }

Answer 1

 $.ajax({
    type: "POST",
    data: formData,
    url: "/Forms/GetJobData",
    dataType: 'json',
    contentType: false,
    processData: false,               
    success: function (response) {
        if (response.success) {
            alert(response.responseText);
        } else {
            // DoSomethingElse()
            alert(response.responseText);
        }                          
    },
    error: function (response) {
        alert("error!");  // 
    }

});

Controller:

[HttpPost]
public ActionResult GetJobData(Jobs jobData)
{
    var mimeType = jobData.File.ContentType;
    var isFileSupported = IsFileSupported(mimeType);

    if (!isFileSupported){        
         //  Send "false"
        return Json(new { success = false, responseText = "The attached file is not supported." }, JsonRequestBehavior.AllowGet);
    }
    else
    {
        //  Send "Success"
        return Json(new { success = true, responseText= "Your message successfuly sent!"}, JsonRequestBehavior.AllowGet);
    }   
}

---Supplement:---

basically you can send multiple parameters this way:

Controller:

 return Json(new { 
                success = true,
                Name = model.Name,
                Phone = model.Phone,
                Email = model.Email                                
            }, 
            JsonRequestBehavior.AllowGet);

Html:

<script> 
     $.ajax({
                type: "POST",
                url: '@Url.Action("GetData")',
                contentType: 'application/json; charset=utf-8',            
                success: function (response) {

                   if(response.success){ 
                      console.log(response.Name);
                      console.log(response.Phone);
                      console.log(response.Email);
                    }


                },
                error: function (response) {
                    alert("error!"); 
                }
            });