You need to be registered with the National Body or one of it's affiliates (for eg; MTBA or CTBAM in Vic).
You can purchase your registration from Werribee if required, but ideally it should be done at the centre at which you bowl. Ask your league delegate which group they sanction the league with and this should clarify things. Your league secretary should have sent some form of paper work to an affiliated body or TBA to ensure your league is registered and recognised for any achievements.
Edi