Are you in a lease agreement or buy your own phone? If you want to cancel a plan just contact Optus direct (LiveChat, Facebook, Optus mobile App etc.) and ask for a payout figure. This will include any outstanding phone amounts as well as any penalty fee etc.
No one can check and all you've done is post your phone number in a public forum for every one to see. Suggest you edit your post (arrow at top right) and contact Optus directly (as the solution to this post tells you to do.)