How to Recover Rent Arrears from a Deposit

Rent Arrears

The letting & management agent failed to pay me the last month's rent of %C2£525 on a 6 months AST. I referred the issue to the TDS who advised that "if the tenants have not paid rent, then this would be deductible from the deposit." The agent was paid a deposit of %C2£525.00 to be held by the Agent until the termination of the tenancy.(PROTECTED BY TDS) The agent has failed to respond to all emails and letters re. the outstanding rent. On applying to the TDS for the deposit to be paid in lieu of the rent, I was told "as the tenants have been unresponsive and therefore not actively advised that they are disputing the deductions, we are unable to accept your application at this time as there is technically no dispute regarding the release of the deposit." What action can I now take to recover the missing rent of %C2£525.00?