Indigo Airlines — Money not Refunded

Address: West Bengal

I had got tickets done from Bangalore to New Delhi. And later got the tickets cancelled.
The cancellation was confirmed by Indigo on 21st December and the customer care executive informed that the money will be credited back to my credit card account within 8 to 10 working days.
I wrote a mail to them again on 8th January and there was response.
I spoke to the Manik (the cutomer care executive) and call continued for over 30 minutes. He did not provide any confirmation not did he allow me to speak to his supervisor or any manager on the floor.
I demand the due principal amount and additional interest / compensation for the delay.