Indigo Airlines — non availability of seats

Address: New Delhi, Delhi

Sir/ madam, i have booked a ticket holding pnr o5qhhl from pune to delhi on 14.10.2017 since december 2016. Now i want to do web check in the flight, but on going through the company website, it is seen that no seat is available for. To select a seat either i have to pay rs. 300/- or to go to airport counter.
As i have already paid the money to the airline then why the web check in facility is not available for me. I also called the indigo customer care for clearance, he also said that you have to pay extra money for selection of seat or either go to airport for check in. It is totally injustice to me as the airline is not providing the web check in facility to me.