Uncheck item from checkboxList which gets selected with querystring onLoad

I have checkboxList which has autopostback true. I have made it in such way in which on SelectedIndexChanged it gets reirected to same page with querystrting. Querystring value gets generated with selected items. Something like this http://ift.tt/2sTyQxs

So when page gets load the Checkboxlist items gets selected where its value is 2000,3000,5000 etc. But here I have drawback is that when I uncheck any item then agin first it executes pageLoad event code & there it finds value which is uncheck & gets selected again. In short unchecked items gets selected again.

PageLoadevent(Checkbox Items gets selected with querystring values)

string PageUrl = Request.Url.AbsolutePath;
if (PageUrl.Contains("price")) {
    string price = Request.QueryString("price");
    string[] priceList = price.Split('|');
    foreach (string p in priceList) {
        if (priceRange.Items.FindByValue(p + "|") != null) {
            priceRange.Items.FindByValue(p + "|").Selected = true;
        }
    }
} 

SelectedIndexChanged(URL created with querystring & redirected)

string pageURL = Request.Url.AbsoluteUri;
string strPrice = Request.QueryString("price").ToString;
if (totalcount > 1) {
    foreach (ListItem chk in brandsList.Items) {
        if (chk.Selected == true) {
            selectedBrands += (chk.Value);
        }
    }
    selectedBrands = selectedBrands.Remove(selectedBrands.Length - 1);

    Response.Redirect((Request.Url.AbsolutePath + "?") + "&brand=" + selectedBrands + "&price=" + strPrice);
}