Unable to activate iPhone 12

I received my iPhone 12 today and followed the instructions provided to set it up, including inserting the new SIM that came with the phone. 6 hours later and multiple calls (& hang-ups when I’m getting transferred), I’ve been unable to speak to anyone who can activate the XM service. I was told to turn off phone, remove SIM and reinsert, to reset network settings (losing all WiFi passwords in the process - ugh), and promised callbacks that never came. Has anyone else had the same issue and how did you fix it (given XM aren’t calling back)?