Letting Agency asking for monthly fee even when the tenant hasn't paid any rent

Letting Agents

I wonder if anyone has any advise on a certain problem. I have been with 'A' letting agency for few years. Last year the previous tenant left. I had to then sign a new contract when the found a new tenant. They told me that the have done all the stringent checks as to his affordability etc. I have left them to manage fully. The new tenant paid the deposit and the first month rent. Thereafter he started making excuses as to why he can't pay, which the agency kept listening. I eventually got a solicitor and applied for S8 eviction. To cut a long story short I am now waiting for the court to give me a date for the bailiffs to evict him after all the usual process you have to go through. It is now eleven months since he paid anything. I have received an email from the letting agency asking me to pay the monthly fee that I would pay, for them to collect the rent etc. I have asked them to cancel the agency/landlord contract with immediate affect which they are refusing to do. Which means that until the tenant is in my property they keep on claiming the monthly fee.
Where do I stand with all this and are there arbitration organisation that can help.