First thing is you need international calling enabled on your service. If it's not currently on, please contact Optus.
From there, you just need to dial the number ensuring you start with the "+" symbol and the Hong Kong country code (852).
More info including rates can be found here: International Calling & Messaging
To successfully port to Optus, you must be the registered account holder with your current provider and your number will need to be active at the time of porting.
Listed below are the porting times / days, between providers. It can take 15 min to 4 hours for a port to complete during these times:
For requests outside of these hours, your service will remain active with your existing provider until the next porting day.
Hey guys, if you'd like to read more about the differences between Messaging and Live Chat, as well as tips to help you get the best experience - see, Messaging explained.
Likely a scam, Chloe136. Did it look like this?