I tested this Program:

/*
  Software serial test
  
 */
#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX
char charbuffer[255];
int inCount;

void setup()  
{
  // Open serial communications and wait for port to open:
  Serial.begin(115200);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

  // set the data rate for the SoftwareSerial port
  mySerial.begin(115200);
}

void loop() // run over and over
{
   byte inputChar;
  int iCount;

  if (mySerial.available()>0)
  {
    inputChar = mySerial.read();
    charbuffer[inCount] = inputChar;
    inCount++;
  }  
 

  if (Serial.available())
    switch(Serial.read())

    {
    case '?':
       Serial.print("Send At...");
       mySerial.print("AT\n\r");
       break;  
    case '!':
      Serial.print(charbuffer); 
      while (inCount > 0)
      {
        charbuffer[inCount] = 0;
        inCount--;
      }
      break;
    }
}

Result:

--> ?
<-- Send At...
--> !
<-- AªCQÔ¤*IIOR†…