Its likely due to APN settings.
Reboot your device, when you are prompt to select Singtel (postpaid) or Singtel (prepaid), please select Singtel (postpaid)
Go to your APN settings, set
APN Profile : Singtel(Postpaid)
APN Name : e-ideas
Go to Settings > Connections > Mobile networks > Access Point Name
Select Settings > Mobile Data > Mobile Data Network