Sue Your Landlord
You tried to be nice, fair, and reasonable, but noooo, the landlord was not on that page. He sees himself as the landLORD, and you'd just better do what he says. Oh, well, you tried. Plan B is you sue him. That's right, you sue your landlord.
If you have not had an initial consultation yet, you really should do that first, so you understand what you can do and how best to accomplish it. The timing is often the most important part, as you'll learn in the initial consultation. Waiting too long, starting too soon, or not having enough to start can be fatal flaws to an otherwise successful lawsuit.
It certainly gets their attention. They never thought you'd put them on defense, but here you are, and they have to seriously face their own liability. Maybe they'll even finally try to settle this with you.