@paweld Hi, I was just reading the "Limitations" section on the official page: https://www.arduino.cc/en/Reference/softwareSerial
You are using a "Mega" board so it seems that with the SoftwareSerial library you can only use a subset of the available pins (actually the limitation is for the RX pin).
Just to confirm, could you try to use different pins as described in the "Limitations"?
Max