Contractor not completing work properly

Hello All,

I have a contractor I hired to renovate my office. The contractor was supposed to do everything in my office including my washroom. The washroom sinks in the middle and now that I have complained they have advised it was an existing condition, and refuses to fix it. They also said it's up to safety regulations. I want a 2nd opinion but they are trying to threaten me by saying that they cannot pay the subtrades until they get the final cheque, and that the subtrades will file a lien against the building owner. To the best of my knowledge a subtrade can only place a lien if the general contractor is unable to pay them (bankrupt, abandonned, etc).

Can someone please give me some adivse how I should proceed? I would like a 2nd opinion about the floor, and dont see how it only became pre-exisiting when I complained.