An apology for mistakes of debiting account

AN APOLOGY FOR POSTING OF ACCOUNT ERRORS

Mr [CONTACT name],
First of all, we announce that we have credited your account in the amount of [amount] covered by the invoice [number].

Secondly, thank you informed us early enough this error

You are absolutely right, we promised there is [number] months of doing you a quarterly billing. So your next deadline of regulation is not in [number] days.

I apologize for the confusion that this may have caused you. Our accounting department has taken its provisions and I can assure you that this will happen again.

Receive, dear Sir/Madam, my best regards.

The Director-General

[NAME OF CEO]