How to send AT command to sim800l with SoftwareSerial
NeoSWSerial would be better for this.  It can read and write at the same time, unlike SoftwareSerial, and it doesn't disable interrupts for the entire character receive time (~1ms!).  AltSoftSerial would be even better, but you can only use it on pins 8 &amp; 9 (on an UNO, different pins on other Arduinos).