HK Renovation gone bad - HELP

I have paid 70% of the bill, and the contractor believes they have completed the job. The works was a full renovation including knocking down a couple of walls, and putting in new partition walls, two kitchens and three bathrooms.

The tiles have been randomly placed onto the wall, not following the pattern, a couple of the walls are not straight and at right angles, exterior walls have been damaged from opening new holes and not re-cemented, the new window was not the design I asked for, and finally, the new kitchen work top and new doors were heavily scratched.

I refused to pay him the final payment and hoping to find another specialist to try and resolve some issues.

The contractor and I are in a dispute over what is the final sum to pay him to settle the matter, he is not willing to negotiate and threaten me by chaining up my gate.

Any advice on who I should contact to help? Any free legal advice? Any renovators to recommend?

Many thanks,
Will