[Here briefly focus on Sample letter to apologize for mistakenly issuing the wrong certificate to the student, client, customer, dealers, franchise, registration certificate etc. You should show an appropriate reason. You can modify this format as your requirement.]
Sub: Apology Letter for Issuance of Wrong Certification
We hope that you are enjoying extremely pleasant health.
This is with reference to our earlier letter no. ABCD/00/ED/123 dated (date), and your letter in response having a reference no. DDD/AAA dated (date) wherein you highlighted a deficiency on our part in addressing the certificate in your name erroneously which actually belonged to other members of the Institute and requested us to issue a correct certificate to your good self.
Firstly, please accept our apologies for the inconvenience being faced by you. To err is human and the mistake is highly regretted. (show actual problem and situation).
We may inform you that we are in the process of dispatching the needful at your designated address. We may request you once again to ignore. We will ensure that you would not be faced with such kind of mistakes in the future. Thus, we welcome health criticism to improve our quality standards.
We are looking forward to continuing professional relationships with your good honor. Thanking you and with profound regards.
Head of Exams,
Institute of Chartered Accountants (Institute name)