I am not sure when the OP (Sankaps) made his reservation. When I tried to purchase a ticket on Dec 26th on Indigo using a US-based credit card, it rejected (two of them). I completed the transaction by getting someone in India to pay with their credit card.

So - they did implement this change although I am not sure how they are protecting themselves by this measure.

Is it true that only Jet and Indian charge different airfares for Indians vs. non-residents and not the other airlines? How does that justify Jet from overcharging?