Set out the tenancy address, deposit amount, move-out date and the deductions you are disputing, then explain briefly why you believe each deduction is unjustified. Refer to supporting evidence such as photographs, receipts, the inventory, correspondence and proof of rent payments, and state the amount you are asking to be returned. Keep the tone factual and send the letter by a method that records delivery, allowing a reasonable time for a response. If the matter is not resolved, you can consider the RTB dispute resolution process; the outcome depends on the evidence and the individual facts, so seek legal advice if needed.