A contractor breaches his obligations of apartment renovation. What to do?

Dear sir/madam,

I engaged a general contractor to help renovate my apartment. It has now been over 4 months. I have major issues with the bathrooms (leaks, incorrect installation). In addition, he has used real cheap quality material which is scratched and has a horrible finish.

Finally, I have a long list of items still not complete. He has been promising for the past 3 weeks that someone will come to review and correct but no one has come and every day I have a new excuse.

I paid him 90% of the money as he talked a good game. I would welcome some advice on the best course of action to move forward.