Air India — date concern

Dear sir,
Good morning. I had booked my ticket through goibibo app from new delhi to bangkok dated on 13 november to 20 november, when i searched app shaw me air india flight available on that days but when i make a payment ticket booked on 12 november to 19 november. Immidiately i called to customer care then they replied we booked your complaint and reply it 24 to 48 hours but no response. I make a call again on 9 october then they replied if you want to change then you have to paid fine and difference. Sir kindly help me i can't pay 12000 more for this booking. Pls help me. I will be highly oblige to you.
Thank you.
Regards
Vijay rana