Dear [ Customer Service Officer],

I am writing to express my disappointment with the [bad service experience] I recently encountered while using your services. On [date], I had an issue with [issue], and I was met with [describe their attitude]. This was very unforunate, as I expected a much more professional attitude from [name].

I hope that this issue will be resolved promptly and I can be assured of receiving better service in the future.

Yours sincerely, 
[Your Name]
[Description of bad service experience provided]
Scrivi una lettera di reclamo per una cattiva esperienza di servizio.