How to control continuous rotation servo via HC-12 rf module
You can't rely on a specific delay being one rotation - especially when you are using SoftwareSerial. SoftwareSerial breaks many things, and anything that uses interrupts (such as the Servo library) gets broken by it. It's a real interrupt hog.

The proper way of doing it is to use a rotary encoder on the servo to report the position (or change in position) so that you know where the servo is. That's really the only reliable method of getting the servo to perform precise operations.

By the way:

mySerial.flush();//clear the serial buffer for unwanted inputs


does absolutely nothing. The operation of flush() changed when the Arduino API turned one. It is now supposed to wait until both the TX circular buffer and the UART TX FIFO are empty. It has nothing to do with emptying any inputs.  Instead you want:

while (mySerial.read() != -1);