i dont see anything obvious wrong with the code, I would start by editing this line:
$query_itemQ = "Update Products SET Products.ProductStock = Products.ProductStock -
$DetailQuantity WHERE Products.ProductID = $idCall";
to:
$query_itemQ = "Update Products SET Products.ProductStock = Products.ProductStock -
$DetailQuantity WHERE Products.ProductID = $idCall";
echo("SQL: ".$query_itemQ."<br>");
this will write the query being executed to help troubelshoot, but really you are asking me here to support something that I have already told you is not supported.