What you have is a rolling service contract with a minimum term. For as long as your phone has service, you still have a contract - but you have now finished your "commitment period".
You can do any one of...
1: Continue as you are, the plan stays the same as does your service.
2: Upgrade your phone if you choose to
3: Change to a SIM-only plan for a lower monthly cost, upgrading back to a phone-plan as & when you see fit.
4: Give 30days cancellation notice, with the option to move to PAYG
5: Port your number out to another provider using a PAC, if you see fit.
