How To Check On Licensed Contractor?

[crs69 0]

I have engaged an interior designer/contractor to perform renovation of my apartment. He has outsourced the construction of a patio roof to a sub-contractor who has performed shoddy work. The acrylic roof cracked, the wooden structure is not straight, the finishing of the roof is horrible.

I have some questions:

1. How can I check if a contractor is licensed? Is it with SCAL, BCA or other authority?

2. In event that a contractor is not licensed or registered, can I reject their work which has been performed?

3. Am I liable to pay a non-licensed contractor for some work which has no quality control?

4. How can I appeal against a non-licensed contractor?

Greatly appreciate if anyone can provide advice to my concern.

Thanks!

Chris