How To Write A Dissatisfied Customer Letter . Acknowledge that it was you who screwed up the order or failed to respond to a complaint “in a timely manner.”. It is, however, unfortunate that you got dissatisfied. 😀 Customer dissatisfaction letter. Letter of Complaint Sample Poor from tukioka-clinic.com Response to a dissatisfied customer complaint. A letter of disappointment can be written in personal capacity (friends, family, colleagues, relatives, social circle) that is informal letter. Sample apology letter to customer.