Rule reminder
A formal complaint letter (lettera di reclamo) follows this structure: (1) Object/Oggetto, (2) Opening formula referring to prior contact, (3) Description of the problem using formal vocabulary, (4) What was expected vs what occurred, (5) Specific request for remedy, (6) Deadline or consequences, (7) Formal closing. Each section has standard formulas.
What is the correct 'Oggetto' line for a formal complaint about a defective product?