Problems with flat freeholder - Croydon Council

We have a flat that we let out to a fantastic LHA tenant - a mother with a young son. The freeholder is Croydon council and we have a major problem with them.

For the last six months there has been a leak emanating from above the property that leaks into one of the bedrooms of our flat. We estimate we have spent 30 hours trying to resolve this with Croydon Council and the levels of incompetence we have experienced - even by council standards - has been staggering.

Despite sending numerous contractors out to view the problem, visiting the flat themselves, and verbally admitting it is their problem to address, nothing has been done.

The leak has caused damp and black mould, which means that the tenant cannot use the room (it should be her baby's bedroom) and as well as the damage to the property, we are very concerned about losing a very good tenant.

Can anyone suggest the best next steps? We just want this resolved and are prepared to spend money to do so.