Indigo Airlines — wrong information provided by customer service

I was travelling to mumbai from usa and then domestic from mumbai to nagpur via indigo airlines within 24 hrs of arrival from usa.
I called the indigo airlines customer service for information about allowed baggage. The representative informed me that since i am travelling international withing 24hrs i have a different rate of payment for my excess baggage which was approximately :
Rs.500 for 5 kg
Rs.750 for 10kg and
Rs.1000 for 15kg

But they never informed that we need to prebook your excess baggage.

I was surprised they charging me rs.300/kg at the time of check in for my flight. Since i did not prebook my extra baggage. I told them i was not informed about pre booking baggage but no one listened to me and i was made to pay rs.5000 for my extra baggage.

Customer service is misleading and they themselves do not have complete information. Very disappointed with the service.