Council Tax HMO

Tenancy Types and Management

I have a property, formerly occupied by 3 tenants on very long standing separate tenancies. It’s an old Victorian house.
The attic is classed as self contained and the tenant is responsible for the Council Tax ( the VOA valued it separately in 2009 as it the facilities are not shared)

The first and second floor are valued as a separate band. There were formerly 2 tenants on 2 separate agreements sharing but I paid the Council tax on this part as the property is classed as an HMO.
Despite the 2 tenants having 2 agreements occupying part only of the property, they were in fact a couple and lived together in all of it. One has died and the other has remained in occupation but refuses to agree to a different tenancy arrangement or agreement because she has security of tenure.
The fact is however, she occupies the whole property.

Council Tax are telling me I am still responsible as the landlord as it is an HMO, even though the whole property is now only occupied by 2 persons, one of whom pays his own Council Tax! In other words, they are telling me I am liable with only 1 tenant because she refuses to sign a new tenancy agreement or move.

I would actually like to evict this person as she is totally unreasonable but know this would be a very expensive and long winded process.
Council tax are telling me that unless I can get her to sign a new agreement I will remain liable for the Council Tax as it is still an HMO. How can this be right?