PROBLEM AGENTS

Tenancy Types and Management

I gave the property to an agent to manage 7 years ago as I had domestic problems and did not have the time to manage.  Now I need to serve S21 and find that the agent has not done certain things. I asked him to return the deposit to the tenant but he said he will leave 5 weeks rent in the deposit and return the rest. 

I told him to serve certain things like how to rent guide by hand but he insists he will do it by email but I read that he cannot do it unless the tenant has agreed in writing.  The agent seems to think he owns the property.  He says they will do S21 but I know it will fail if they do it.  They want to be in the driving seat.  Dont agents have to do what the land lords ask them to do?