@Ikram39 If the number has been out of credit for 6 months you may not be able to get the number back as they are put back into the pool to be recycled.
If you need further assistance Please message Optus Support 24/7 from the My Optus app. If you do not have access to the My Optus app you can use social media to contact Optus Support, please send a PM to Optus on Facebook or a DM on Twitterand include in the message you do not have access to the My Optus app.
I am not an Optus employee. If a reply helps please give a Kudos and when an issue is solved please mark as solved.