I am the contractor. I was to build a inside wall. After job was done, later customer was not happy. Without informing me, hired another contractor to work on wall because they were not happy with work. And because they were unhappy with my work, they want me to pay the new contractor for work that has been done on wall because they say it was my fault. Can they make me and by law were they suppose to inform me first before they hired other contractor.

Do you have a written contract? If so, what does it say about approving the work? Did they inform you they were not happy with the work and give you a chance to fix the issues?

They have every right to hire a new contractor without informing you. There are no laws that I am aware of that would prevent that. But laws vary by area so you should check with your local Consumer Affairs agency.

You said they were not happy. Did they inform you they weren't happy? Did they explain why? Did they give you a chance to fix it? I don't think they can legally hold you responsible for the costs unless they first gave you notice of their unhappiness and a chance to fix it. However, if they did inform you and you told them nothing was wrong and wouldn't fix it, then they can probably hold you responsible. I would expect that the second contractor took pictures and would be prepared to testify of the problems.

So what happens now is you tell them

When you were finished, before they paid you, where they unhappy, did they tell you?

They would need to inform you and give you a chance to redo the work normally, but if your work was to such a poor standard, that other contractors would testify of the poor workmanship, perhaps they would not have to allow you a chance to redo.

Also if you do not have proper licenses, that could be an issue (I am sure you do, just a lot of unlicensed ones running around)