Are they just holding off because it will be expensive?
They have to fix it. They’re in breach if they don’t. Has it been more than 2 months since you asked?
You could get orders from NCAT. That could be longish and painful and in mean time you still have your problem and water getting in.
Or just get a quote, send it to them, and add it to your list as evidence.
I’m pretty sure that not maintaining the building can also invalidate insurance.