Indigo Airlines — Unethical deduction of cancellation charges

I had booked return ticket for 4 persons for ahmedabad - Dharamshala for 12th and 19th May vide PNR GUT74V and U7NEGA on 23 Apr and paid by credit card. My onward journey for 12th was cancelled by Airline due to closure of chandigarh airport and full refund was approved. However Indigo approved my refund with deduction of Rs 14216 for the return journey. This is highly unethical as we could not have performed the return journey as the onward journey was cancelled. Why two seperate PNRs are issued for return journey booking is not understood. I demand that full return be issued for the return journey also