I am having some trouble with my SIM800L module. Basically I set the DTR pin to high and then used AT+CSCLK=1\n to put the module into sleep mode. Then, to wake it up I tried to set the DTR pin to low and send AT+CSCLK=0\n to the module but nothing happened. I have also tried to call the module and send AT+CSCLK=0\n again, but it still didn’t work. My power source showed a rise in current usage but it went back to sleep right after the call ended.
You are not doing it fast enough 
Keep sending AT commands in loop when it wakes up. Then when it responds OK, Send the AT+CSCLK=0 command. I would advice to use CSCLK=2.
But does SIM800L support CSCLK=2, it doesn’t say anything about it in its datasheet. Thank you!