Dear Mr. Brown,

We have recently received complaints from customers about your USB flash disk. The disks are clearly not satisfactory.

They are part of the batch of 600 supplied against our order number 4698 dated 12 April. Some customers complained that the disks broke down and they lost all the data shortly after they bought them. We have checked all the faulty disks and found that neither of them worked.

The complaints we received relate only to disks from the batch mentioned. Customers who bought disks before have been pleased.

We wish to return the unsold balance, amounting to 560 disks, and to have them replaced with disks of good quality.

We look forward to your reply and to the arrangements you wish us to make for the return of the disks.

Yours sincerely,

Richard Carlson

Analysis

这是一封写给生产商的投诉信。信中说明了产品的订单号、订购日期及出现的问题，继而提出解决办法。语言表达简练、明确，语气也较礼貌。