Restoring an enameled cast iron stove top surface (porcelain?)

Q. I own a year-old Imperial range with cast iron grates that have a shiny, enameled porcelain finish. I have cleaned the stove top with soap and water as well as oven cleaner ⇦ on eBay or Amazon [affil link] , which works well on the baked-on food. However, my housekeeper used something else on the enameled porcelain finish, which has left large dull blotches all over the enameled porcelain finish. It looks horrific! I called the manufacturer, and they could not offer a restoration remedy. They did say this happens often and were willing to sell me new grates ($675.00 + tax and shipping). Does anyone know if any product or service that will restore the shiny surface to the black enameled porcelain finish?