There's already a thread for that with lots of people venting frustrations - https://community.stadia.com/t5/Stadia-General/Ordered-6th-of-june-yet-to-recieve-a-code/m-p/389#M16...
When did you order? I ordered quite late on (July 30th) and have had the hardware for 24 hours. Frustrating to say the least!