Security Deposit

If the amount is substantial, visit to the landlord with a friend and demand for refund of such deposit, use such recording devise if any to record the conversation, wait up to the due date and issue a notice demanding for such payment within one month.  If all normal efforts fail, calculate cost benefit analysis and then entrust this to advocate.

Where is the tenanted premises, how much is the amount of security involved and what is the plea taken by landlord for non-refund in full ?

Amicable settlement may be preferred.