Write a letter acknowledging the merchandise returned for repair.

Dear Sir,


This is to inform you that the (product name and model number) that you mailed to us for repair was received on (date). We will be returning it to you as soon as the necessary adjustments are made.

We regret that you experienced a problem with our product and want to thank you for purchasing (product name). We shall take care in future that you don't encounter such problems. 

Thanking you.  

Yours truly,