Can’t call out or receive calls (iPhone 11 pro)

[BellePumpkin]

I’ve just switched from EE to O2 about two weeks ago. I feel calls used to work fine, but until about 3 days ago, I get no rings calling someone and it’s completely silent when someone calls me. If i answer a call there is nothing then the call fails a few seconds later.
I’m really frustrated and tired with this. I’ve reboot the phone and plan to try my sim in another phone in our household who has also just switched to O2, but their calls are working perfectly.

[MI5 · Accepted solution]

@BellePumpkin 

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