Citi Bank — Need bank-certified letter for account closure

Address: Citibank na 27, central market punjabi bagh new delhi:110026

I have stopped using CITI bank account for a while now and invested some money in mutual funds using CITI bank account as primary account back in time. Now I moved to another bank, however when I'm trying to redeem the money the fund says it will go to CITI bank which I no longer have access to. To change the bank account, I would need CITI bank's certified letter for account closure. Please share it on urgency.

Details -
Name - Vishesh Gupta
Account - [protected]
IFSC - CITI0000031
Email - [protected]@gmail.com