Why was an SMS received from CDSL informing debit of T-bills(all) when a sell order was not placed?

Why was an SMS received from CDSL informing debit of T-bills(all) when a sell order was not placed?

Such type of SMS is received at the maturity time of T-bills. When the T-bill matures, the units are automatically debited from the demat account and the maturity amount is transferred to the primary bank account linked with the Jainam. CDSL sends a message whenever there is a debit of shares, mutual fund or G-sec holdings from the demat account. The transaction will be updated in My holdings under Polaris and Comet in Space at Jainam.