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Hi @Jo3 . Is your phone configured for LTE (phone calling on 4G)?
TPG 3G network closed some weeks ago. Telstra 3G network will close end of June.
@Jo3 . Check the user manual for your phone. Does it mention LTE?
In the phone app settings, any option to enable LTE?
Check online or with Apple whether your phone can do LTE or not.
Your phone uses 4G for internet when wifi is off. If you try to make a phone call, does the indicator change?
@Jo3 . Americans call it cellular data, we call it mobile data.
Best bet is to contact Apple support whether your model supports LTE calling. Include the full model number of the phone.
You can look here: https://support.apple.com/kb/SP779?locale=en_AU
@Jo3 . When you switched to TPG, did you contact Telstra at all? Not that you need to at that point.
Is Telstra still billing you?
Did you keep using the Telstra sim card until it stopped working?
Or did you insert the TPG sim card when it arrived?
Anything happen if you put Telstra sim card in?