Thanks for your post on our Community Forums and a very warm welcome to you!
Sorry to hear of the issues you've been having with your mobile phone services
Can you tell me if you've been able to perform a manual network search on the handset? Can you also try switching roaming off on both the handset and self-care account to see if this will allow you to make calls?
If you can also remove and replace the SIM card, as well as trying this in a different phone, this will allow us to rule if this is a SIM card fault.
If you do however have an old red SIM card, it may be a case of us needing to update your SIM card to one of our newer purple SIM cards.
Please come back to us so we can ether assist further, or let us know if any of the diagnostics advised have helped