If I were you I would have contacted the company as soon as I saw the soot inside my house.
Thier insurance should have cleaned up the mess.
They do make a cleaning spong that removes the soot from ceiling but, it should be done by a pro that is paid for by company you hired.
You might want to contact the company and tell them you are not happy and that you want this cleaned properly!
Ask them what method they used to clean the ducts, (I bet they sucked the dust from one end of the house to the other because it got out at every possible opening. let us know)
Also ask them what were the chemicals they used.
If they say no, I would call my own insurance company and talk to your representative about what you can do. They will often pay to get the work done and then go after the company you hired to get reimbursed.