Indigo Airlines — complaint regarding rescheduling the flight

I am traveling varanasi to bangalore and my pnr no. Is u9h35c where i have received a message stating that my flight timings got rescheduled after that when i have called to indigo customer care those person are telling i can't able to change the timing as per the rules if a customer received a resheduling msg he can change the timings as per his convenient time.
Last time in the month of april same thing happened and i have rescheduled the flight as per my convenience. Now indigo team is telling that last time was exception. I am not understanding that what is the problem.
I want a solutions and i will not leave like this.