UK Landlord Forum / Life

I own a leasehold flat that I sub-let to a tenant.  I have been charged repeat sub-letting fees by the Freeholder's agent (Simarc) since I bought the flat, but the tenant has remained unchanged, and there is no provision within my lease for the Freeholder to charge repeat fees.  I queried this, and after putting up a fight they eventually agreed not to charge me any further fees (while the tenant remains the same), but they have refused to pay back the charges I have paid in the last three years, despite a legal opinion from the Leasehold Advisory Service that the charges were a "serious breach of the law" and should be repaid to me.   Anyone got any advice or thoughts on this?

Small claims court.