Lost Wnidows XP product COA when service was done

does anyone know who I need to call. During the last servicing (just before my warranty expired) of my laptop (which came with Windows XP Media Center) I had to send my computer in to get repaired, after the tech guy that came to my house (dispatched from dell) couldn't fix it. Before I sent it in I didn't think to write down the product key on the sticker under it. so when they replaced the underside of my notebook (the side with the sticker) I lost my product key. My hard drive recently got wiped so now I don't have a working installation of windows XP to find it on. I was wondering who to call, if there was anyone I could call(before trying to get a new one) in order to get a copy of my old one. Thanks for the help.