1. A method comprising: establishing, with a service control gateway positioned between an access gateway for a mobile access network and a packet data network that provides a service, a session by which a mobile device is to access the service; determining, by one or more processors of the service gateway, that the service gateway has incomplete information to activate usage monitoring of the service responsive to receipt of a message to activate a charging rule that includes a request to activate usage monitoring for a service identified by an identifier without having received any message associating the identifier to the service provided via the session: and in response to receiving an indication to activate a charging rule having an incomplete indication to activate usage monitoring with respect to the service provided via the session, rejecting the charging rule.