State the purpose of the letter upfront. Provide a concise summary of the issue and circumstances that led to the need for a refund. Explain why you believe you are entitled to a refund, citing any policies, procedures, or previous communications from the bank that support your request.
I am writing to tell you that the payment was an unauthorized transfer. My bank account number is x-x. My account statement or other notification sent by you shows that an automatic payment was made to Company name. However this payment was unauthorized.
Obviously, these types of losses attributed to overpayments are both material and significant. Additionally, it is the responsibility of all stakeholders to return any overpayment because every buyer is a seller at some point.
Let them know as soon as possible and immediately offer a way to resolve the overpayment, either as crediting their next invoice or issuing a credit.