Indigo Airlines — Technical error in website which costed me additional 800 rupees

I booked a flight under 6E509 student for 11th April from BLR to NGP. I explicitly remember that while booking the flight I ticked multiple times and agreed to all the terms and condition for the student discount (25 kg baggage allowance) but at the time of booking and also at the time of checking in that discount wasn't availed. Due to this, I had to pay an additional 800 for my baggage and the worst part is I have to travel from the same PNR no. on 31st may from NGP to BGR. I need my 25kg allowance for that particular flight. kindly look into the matter.