SIM808 module: GSM location command (AT+CIPGSMLOC=1,1) giving wrong value after execution of sending message command (AT+CMGS=+91xxxxxxxx)
It might be due to the command giving the nearest cell tower location. And for sending SMS it might be shifting to a different cell tower depending on your network. This could maybe be easily checked using a different cell provider or as you said its working at your home so I believe I am correct in assuming this is the answer