Did you provide the correct address to the Adsense? If you provide false address to Adsense, you won't receive an envelope that contain the PIN. So you can't run the Adsense business. OR Is your home a person for receiving the envelope form postman while you go away?
Contact customer support with your proof. There might be some fault with your account, otherwise I never heard this type of problem.
Contact support, and make sure you have provided them the correct information. Also check for gnomes, they have been know to steal mail.
If you've requested your maximum of 3 PINs and haven't received any of them within 4 weeks of your last PIN request, sign in to your account and you'll see a notice on your Home page with further instructions on how to send us an official document proving your address through a contact us form.