Request for additional information
Re: Your letter of xx/xx/xxxx
Dear Mr./ Ms. x,
Thank you for your letter.
Unfortunately due to lack of details in your letter we could not locate the relevant project in our files.
kindly supply us with more information about this letter such as our reference number, project name, etc.
Enclosed is a copy of your letter.
We look forward to hear from you.
<name of contact person>