Why was an SMS received from CDSL informing debit of T-bills when a sell order was not placed?
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 Zerodha. CDSL sends a message whenever there is a debit of shares, mutual fund or G-sec holdings from the demat account.
The SMS will read CDSL: DEBITED IN A/C *xxxxxxxx 100 TREASURE BILL OF GOVERNMENT OF INDIA TOWARDS REDEMPTION ON 18/01/2019. CONTACT YOUR DP FOR MORE INFORMATION.
To check the primary bank account linked with Zerodha, see What is a primary bank account with regards to my Zerodha account?