@Islaface I am guessing you are hoping to get your old number phone back? After about 6 months of inactivity numbers are returned to the pool to be recycled. Numbers can be recycled in different ways such as being issued to wireless broadband sims. You might call your old number and get a message this number is unavailable .... and you think okay it is available you get a similar message if the number is assigned to a mobile broadband service.
If your old number was originally issued from a different Telco and you has ported the number to Optus the number would go back to the issuing Telco.