Reinstalling Office 2011

Any idea how to reinstall Office 2011 for Mac when tech support tells you that the product key you have is not valid (which is also displayed when I try to reinstall it, so helpful!) and I am told there is no way to get the correct product key. I currently have the original box, original receipt, pin, etc. The product key worked the first time I installed the product however it does not work when I try to reinstall it. Currently I have $127.00 worth of a paperweight. Help, please.