SIM 7000e shield and Arduino UNO

Question

I'm pretty new to Arduino, especially in terms of shields for it. I'm using a SIM7000 shield for Arduino from DFRobot. I was working on project to send SMS to me when something happens, for example if the temperature is too high, a simple project.

So for a week everything was fine, the program worked, and my setup had an external power supply 12V plugged in and at the same time had USB connected from my laptop to Arduino to program it. As I said this worked fine for a week. This shield is said to need 7 to 12 V to work. And today something happened.

I was working with this project as usual and something happened and my Arduino poofed, the 5V regulator started smoking, so of course I instantly unplugged everything. I removed the shield from Arduino, and checked whether the USB worked, but it didn't, no diode is lighting up and the regulator is slowly heating up while the USB is connected. I don't know exactly what happened. As far as I remember I had 12V plugged in and USB wasn't, so I plugged the USB in and this happened. I don't know if something like this should happen as I'm rather new to Arduino. If someone could tell me what I did wrong, I would be very happy to know.

But as my Arduino is rather dead, I'm wondering whether the SIM shield could be damaged too. I couldn't check it as I didn't have cables, only a charger and this shield only has a micro USB port to connect. So my question is, could that shield be dead too? Or is it rather impossible?

This is the shield I am using