No cellular calls

I have a I phone 16 pro max was not the three network not I have ported my phone number to Lebara and inserted the sim . All WiFi is working I think but I cannot make normal phone calls unless I use WiFi calling . Can you help

have a I phone 16 pro max was not the three network not I have ported my phone number to Lebara and inserted the sim . All WiFi is working I think but I cannot make normal phone calls unless I use WiFi calling . Can you help