Go First Airline - Flight left before departure time

I booked a flight from Bangalore to Mumbai on ** Jan'**. It was supposed to take off at *:**. Firstly it was supposed t take off from gate **. When I reached the gate they told me the gate has been changed to **. I reached gate **, the Go First personnel told me the flight had already left. I reached ** mins prior to the take off time, there was no announcement or message the gate has been changed and the flight took off way before the scheduled time leaving a passenger behind. This is highly unethical and unacceptable and no Go First personnel was ready to listen. Is this the kind of service this airline provides.