How do you write a letter to bank manager for block of ATM PIN?

If you can either visit your bank branch or telephone them that would be quicker. If you wish to send a letter, you will need to include your bank account number, the reason why you want a change of PIN and of course your contact details such as your address and telephone number. You cannot block a PIN number but request a new one to be posted to you. You can stop the card should the details of your PIN be in the hands of another.