Instructions:I don't know if this will work, but I have two Google accounts. The one which I don't use normally got offered this offer. So I tried using the web address from the link on the page on my normal account, and it worked!
So give it a go, and if it doesn't work... nothing lost. Except time. Can't get that back, sorry!
Make sure you are logged into your Google Play account before you click this link. https://play.google.com/redeem?code=KZQYKE4HMW6UDK6RJZQQ5H6