After many emails with Arduino support and no solution that would work I decided to give up on the Arduino Sim. I did get it to function for a short time by changing my code to read #include "MKRGSM.h" instead of #include <MKRGSM.h>. Why the quotes instead of brackets? Who knows why it stopped working again? I purchased a Hologram SIM which seems to be working reliably. Arduino needs to step up their game here! Why are you selling products that don't work? It's very frustrating for beginner programmers not to be able to find solutions to their problems.