If you would like to confirm that you have received a complaint, here is a sample acknowledgment letter for a complaint received.
To [Recipient name]
Dear, [Recipient name]
We have received the letter regarding [Issue] and we assure you that this complaint will be taken into careful consideration. You will receive a notice once the necessary steps are adopted to resolve the issue. Your convenience is our priority and we will deal with the issue at the earliest.
We thank you for bringing this problem to our attention and we will do our best to make improvements. Your feedback is valuable to us and rest assured your complaint will be addressed as soon as possible.
We regret any inconvenience you had to face.