Bind parameters to my custom reportviewerwebpart and refresh it

Question

I'll try to explain my problem in the easiest way I can, since even for me it is difficult to understand.

I've created a custom web part in which I have two columns: a datalist and a few buttons on the left, and my reportviewerwebpart on the right.

I've created a class to build my custom reportviewerwebpart, code below:

public class CCReport : ReportViewerWebPart
{
    private string herdId;
    private string prvCd;
    private string breed;
    private string heifer;
    private string reportType;
    private ReportParameterDefaultCollection paramCollection;

    public string HerdId
    {
        get
        {
            return this.herdId;
        }
        set
        {
            this.herdId = value;
            paramCollection.Add(new Microsoft.Reporting.WebForms.ReportParameter("herdId", herdId));
        }
    }
    public string PrvCd
    {
        get
        {
            return this.prvCd;
        }
        set
        {
            this.prvCd = value;
            paramCollection.Add(new Microsoft.Reporting.WebForms.ReportParameter("prvCd", prvCd));
        }
    }
    public string Breed
    {
        get
        {
            return this.breed;
        }
        set
        {
            this.breed = value;
            paramCollection.Add(new Microsoft.Reporting.WebForms.ReportParameter("race", breed));
        }
    }
    public string Heifer
    {
        get
        {
            return this.heifer;
        }
        set
        {
            this.heifer = value;
            if (this.heifer != null)
                paramCollection.Add(new Microsoft.Reporting.WebForms.ReportParameter("visibleId", heifer));
        }
    }
    public string ReportType
    {
        get
        {
            return this.reportType;
        }
        set
        {
            this.reportType = CCConstants.REPORT_PATH + value + ".rdl";
            this.ReportPath = this.reportType;
        }
    }

    public CCReport() { }

    public CCReport(string reportType, string herdId, string prvCd, string breed, string heifer = null)
    {
        paramCollection = new ReportParameterDefaultCollection();
        paramCollection = this.OverrideParameters;
        this.ChromeType = System.Web.UI.WebControls.WebParts.PartChromeType.None;
        //this.PromptAreaMode = CollapsibleDisplayMode.Hidden;
        this.Height = "693";
        this.HerdId = herdId;
        this.PrvCd = prvCd;
        this.Breed = breed;
        this.Heifer = heifer;
        this.ReportType = reportType;
    }
}

When I open the webpart this is my LOAD:

protected void Page_Load(object sender, EventArgs e)
    {
        SPWeb web = SPControl.GetContextWeb(Context);
        //user = new CCUser(web.CurrentUser, Request.QueryString["noTRO"], Request.QueryString["prv_cd"]);
        user = new CCUser(web.CurrentUser, "2633", "04");

        // Get user's race types and bind to the DropDownListRaces 
        if (!this.IsPostBack)
        {
            DropDownListRaces.DataTextField = "Value";
            DropDownListRaces.DataValueField = "Key";
            DropDownListRaces.DataSource = user.breeds;
            DropDownListRaces.DataBind();
            DropDownListRaces.AutoPostBack = true;
            DropDownListRaces.SelectedIndex = 0;
        }

        rv = new CCReport();
        hg = new CCHeifersGrid();

        // events
        hg.SelectedIndexChanged += new EventHandler(heifers_SelectedIndexChanged);
        hg.SortCommand += new DataGridSortCommandEventHandler(heifers_SortCommand);
        //DropDownListRaces.SelectedIndexChanged += new EventHandler(DropDownListRaces_SelectedIndexChanged);
        RadioButtonListReportType.SelectedIndexChanged += new EventHandler(RadioButtonListReportType_SelectedIndexChanged);

        // heifers grid
        hg.DataSource = user.getAnimalsByRace(DropDownListRaces.SelectedValue);
        hg.DataBind();
        PanelHeifers.Controls.Add(hg);

        // reportview
        rv = new CCReport(RadioButtonListReportType.SelectedValue, user.herd.id, user.herd.prv_cd, DropDownListRaces.SelectedValue);

        PanelReport.Controls.AddAt(0, rv);
        UpdatePanelReport.Update();


    }

MY PROBLEM:

First time entering the webpart: it doesn't load the graphic(report) even though I can see my parameters on my PromptAreaMode. I have to to change my dropdownlist (postback = true), so it shows up on the page, but... after every change I do on my dropdownlist, it must also changes the report. It doesn't even change the parameters on the PromptAreaMode, even though when debugging I can see that the change is done correctly.

PLEASE CAN SOMEONE HELP ME? I need to finish this!

Thank you!!!