Air India - Refund not received

I have booked return ticket of Air India flight for Ahmedabad to Toronto sector for Travel dates **th April to **th May.
Now Air India has cancelled this flight.
So I demanded refund of the paid amount, but they are denying refund and telling that they have kept the refund amount into their credit shell and I can use it to book future travel.
I do not have future travel plans for canada as of now. As flight is cancelled by Air India, I must get full refund of my paid amount.
Also according to the CIVIL AVIATION REQUIREMENTS SECTION * – AIR TRANSPORT SERIES ‘M’ PART II, under point no. *(f) it is clearly mentioned that,

"The option of holding the refund amount in credit shell by the airlines shall
be the prerogative of the passenger and not a default practice of the
airline."

So I am demanding full refund of the paid amount.