Hi @quang1997, you can reach the Customer Care team on +61 2 8082 5678 between 8am and 7pm AEST. This number is a free call from an Optus mobile phone with International Roaming enabled.
If you're needing assistance with anything, please feel free to reach out to us by a private message via our Social Media pages (official Optus Facebook page or Twitter page) and we'll be happy to help.
Alternatively, you can reach us on a smart device via our Messaging service on the My Optus app 24/7.
