It would be worth asking this question in the forum search facility at the top of the page @PH12 where you will be able to find previous threads asking the same question.
Unfortunately, if it's PAYG, the disconnection time period is 180 days since the last chargeable connection, if it's been any longer, the number will be disconnected from the network and impossible to reconnect.
For pay monthly, it's generally 3 months since disconnection and it would involve reconnecting the contract.
