Specify the purpose of the authorization letter, such as granting access, making changes, or closing the account. You don't need to write any letter, additionally, no one would entertain withdrawal on the basis of a letter, the mandate should be clear.Contact your bank for a power of attorney form. Call and write the company. Tell the company that you are taking away your permission for the company to take automatic payments out of your bank account. Here we share Authorization letter to bank to Transaction, Collect Document, Withdraw Money, Wrong Transaction, Withdraw money, etc.