That’s bexause you have this line:
BlynkTimer timer; // Announcing the timer
at the very top of your code before this line:
#include <BlynkSimpleSerialBLE.h>
which tells the compiler to use the Blynk library which contains the code that makes BlynkTimer work.
Also, these two lines conflict with eachother:
You have also managed to get yourself totally messed-up when it comes to your serial ports. The Mega has 4 serial ports, so there should be no reason whatsoever to use SoftwareSerial to create an additional serial port.
Maybe you should read this recent post:
:Pete.