If a client wants to dispute a transaction, he must contact the merchant first. If the operation is not complete, you should wait until it is finished first.
If this action has no solved the disputed transaction in Westpac, you can contact the bank in Internet banking or the mobile app.
You can also phone 1300-651-089 or +61-2-9155-7700 (if abroad).
In the same way, you can contact the bank if you have Westpac credit card disputes.