Re: Adwords Express
Billing for AdWords & AdWords Express can be found within the AdWords interface. Do you see any alerts/notifications in the account about billing? There could be a few reasons like insufficient credit balance (for manual payments) or CC not chargeable (for automatic payments) due to which account may stop serving ads. I'd suggest checking the Billing tab to understand if there are any payment issues.
Feel free to write back with questions.