Returning the deposit

Possession - Section 8 and Section 21

My agent had got more than 5 weeks rent but it was before the new rules came.  Tenancy started August 2017.  I asked him to return the deposit but he doesnt like it all .  Said my deposits agreed that all thats needed was to keep 5 weeks and return the rest.  Agent says tenant has not given bank details to my deposits to return.  Agents legal advisers say its ok as it was beore the new rules.  How ever; I want to cancel the agency and manage either myself or give a different agency possibly a national one unlike this small family owned agency.  How do I get conrol of the deposit to return it?.  My deposits say the contract is between my agent and the tenant and they cannot discuss with me. Can I just leave the deposit lying there withthe contract being between them and the deposit scheme even if the agent is not managing any more?.  The agent does not respond to my e mails now and the tenant is playing games.