“You have less than one month to verify your PIN, otherwise your ad units will stop displaying ads“.
I bet this message makes you a little nervous. How long it takes to receive address verification letter from google. They clain it typically takes 2-4 weeks, but it may take longer depending on your location.
The fourth week is ending and verification letter for google adsense is nowhere. If you running out of time request a new address verification letter for google adsense otherwise they stop displaing ads in your page.