Cannot make non-US calls while travelling in Europe - help?

Hi! I am travelling in Europe and I have Magenta plan with the International Data pack. I can make calls to the US and via FaceTime but when I try and call a number in Europe it will not connect. I noticed that if I have 5G that when I hit call the 5G drops and so does the call. This is really frustrating as I tried to call the taxi I had booked from the airport and only had cell signal (no WiFi) and was completely stuck with no way to communicate to the taxi. This has happened now in Italy and Montenegro so I don't think it is because of location. Any ideas? I have VoLTE enabled, 5G Auto and I have tried with 5G standalone on and off. Many thanks!