Re: Offer Code
Sorry you haven't seen the credit applied to your account. You have to enter the offer code (first), then spend the $25 or fulfillment requirement mentioned on the voucher. Sometimes it takes a few days for the credit to post.
More details on this at Google Voucher Support. If you don't see the credit appear after you fulfill the requirement mentioned in the offer, it's probably wise to give AdWords a call.
The link below will give you their support number. Just use the drop down to choose the country you are in. http://support.google.com/adwords/answer/1385067?hl=en
I hope this is helpful. Good luck with your new campaign!
Stefan T. Martinez
-- Not an AdWords expert, just a student eager to learn more...