When you log in for the first time it will show as a flashing button on the left. You have to click on it to redeem it. If it is unclickable and you are positive you did not redeem it today than send in a ticket for a bug report using the "Contact Us" link at the bottom of the page.
however make sure first no one else has access to your account. If you share your account then that other person may be using it on you. In addition account sharing is a no no.
As for vouchers make sure you work on every quest you get, especially the dailies. They give you lots of vouchers and I have been doing this to keep my outfits renewed when they expired.