“Letting Agent controls the money” Every day is a school day.
Check your tenancy agreement, a decent one will provide for return of deposit unless notice of bona fide dispute.
Otherwise, the LA can release the deposit on court order, and given the circumstances I would be going for a summary judgment.
Also check your RR agreement, as you undoubtedly paid them fees for setting up the agreement you have a contract you make be able to pursue them under – although it probably exclude this action.