We're sorry. In rare cases, Google Play's processing fails and the purchase is not completed correctly.
Please restart your device, then open the menu (≡) → "Premium Service" and tap the "Restore" button (for users who purchased before).
If the Premium Service is still not active, choose a plan and go through the purchase again. With the same Google Account you won't be charged twice; if your earlier purchase went through, it will simply be applied.
To check whether the purchase was completed, tap "Subscription Status" on the "Premium Service" screen. It opens your subscriptions in Google Play.