I have invested 40k in the 91-day T-bill. However after the maturity period got over, I got only the principal amount debited back to my account, not the interest. How long will it take for the interest amount to get deposited?
What interest? AFAIK, there is no interest on T-Bills.
They are zero-coupon bonds sold at a discount to the face-value (and later upon maturity, redeemed at face-value).
Returns from T-bills are in this form of capital-gains (and not any interest).