Sample regret letter format for wrong bill

To
Address
_____________________________
_____________________________
_____________________________

Dear Sir/Madam,

We are in receipt of your letter of _________________, and we deeply regret the inconvenience and embarrassment caused to you on account of an oversight on our part. Your account has been credited for the value of the ______________in question. Please accept our abject apologies.

Thanking you for your patience and assuring you of the best of our attention.

Yours truly,

Your Name
Company Name

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