Can't communicate with SIM800 module
This is widely happen problem - serial communication with SIM800L stopped working.
You can do reset, but in my case it didn't help: on powered SIM800L module shortcut "RST" pin with the ground for half of second - unit should reset and restart. I think it's defective architecture/firmware, but unfortunately SIMCOM dropped support for this model, so best advise is to avoid SIMCOM until they study how to make quality products.