Make sure that you've run through the first reference first. Do so quickly. If someone has hijacked your account - typically by guessing your password - then you may be buying adverts for a scammer.
If that process fails, there is an Account Recovery Process, recently referenced by AdWordsPro.Sarah... The second reference. It's more onerous as you have to prove who you are through details you've given to AdWords - such as credit card numbers and precise payments.