Ongoing leak from upper flat for 4 years- wet and dry rot

Maintenance

There has been on ongoing leak on and off for 5 years from the flat above the one we rent out (also rented out). We have spent much money painting the ceilings, and recently replacing ceilings and treating the wet and dry rot in the ceiling caused by the ongoing leak. This has cost around £6k plus considerable incovenience to our tenants.

The landlord of the upper flat has only ever answered the phone about 3 times in the 5 years and is very unco-operative. We and the managing agents try to call several times after every leak. We leave voice messages and text messages and he never responds. The leak happens every couple of months.

We do not know the landlord's address and it is not on the title deeds (only the address of the flat he rents out). The tenants in his flat do not speak English and can only provide us with the telephone number he never answers. There have been some attempts from him to fix the leak (presumably his tenants have managed to tell him) and it seems to work and then a couple of months later it happens again.

Unfortunately the owner of the freehold is an 'absent landlord' so there is no way we can get the freeholder to assist with this.

Is there anything we can do to force the landlord to repair his property so the leak stops? And if so I presume we would need his address? How would we find that out (we have asked him many times but he has not provided it)?