It seems that the website mentioned by you is indeed an official reseller for Microsoft products. After you purchased the product, you should register it on the official website. In this matter, try to read the following article. There the developer explained why you should activate your products. If you want to purchase another Microsoft Office product, I advise you to use the official website for this. Create an account and make an order. By doing this, you can contact a staff representative to help you with your old copy of the product, as well as guide you in purchasing a newer version.