Water ingress, leaseholder not taking action.

Maintenance

Flats: The Bathroom above mine is leaking waste water in my ceiling. The leaseholder above me is aware but keeps fobbing me off, by promising repair but nothing happens. I have reported to environmental health but they too are not interested, saying its a civil matter (enough though i said it was a covid issue)
This is clearly a breech of the lease, luckily I am also the outright Freeholder as well as the leaseholder of the flat the water leaks into. Given the softly and nice approach is not working what is the next best action.
Also the same leaseholder has made unauthorised alterations (concrete/ screed floor on timber joists to form wet room, which is cause of the leak). I know there is a loan on this flat, should i write to the lender?