What troubleshooting have you done so far? Please do the following troubleshooting below. If you're done with the step please skip.
Dial ##002#+call to remove all active diversions on the handset.
Power cycle the handset. After turning off the handset, battery should be removed. Put it back after at least 10 seconds, then turn on the handset. For handsets like iPhone or any handsets which don't have a removable battery, restart must be done.
Complete a manual network selection. You may need to select another network, then select Vodafone/Optus/Roaming and then turn the phone off and on again.
Change Network Mode/Preferred Network (from 4G to 3G or vice versa).
Do isolation test try a different handset and/or SIM card