Alex, the item that you purchased is a cover for a #mezuzah but not the mezuzah itself. The mitzvah is about the handwritten scroll, not the case around it. This is analogous to having a Torah cover in a synagogue without a Torah scroll inside. We can view this as an opportunity to learn about a mitzvah. The next step would be to order a #klaf (kosher scroll) from your synagogue gift shop or local Jewish book store.