I'm going through a similar thing: they want $4500 by May 14 for extra dryrot repairs after their renovations last year found extra damage, but we have the "option" of going on a payment plan. I'm furious, but if I have no other choice, there's the payment plan option which is why I feel I wouldn't have a case if I got a lawyer.
Not being allowed that has got to give you some kind of case to fight this.
Currently playing: Skyrim, Hearthstone
Training log: https://powpowpunishment.blogspot.com