My account was charged, I got my Stadia hardware in the mail, but I can't play because I have yet to receive a code.
Check this thread. Seems to be a common issue and not much information coming out from Google.
https://community.stadia.com/t5/Stadia-General/Ordered-6th-of-june-yet-to-recieve-a-code/m-p/255#M86