Bad Builder

I purchased my first home and had gotten advice from Team Bark to hire a builder and I did. His name is Jerome Chetty from Inkosi Building. He messed up my buidling and charged me a huge amount but now that I require a COC Plumbing certificate, he refuses to give me one. Please help. He isn't registered with the NHBRC nor approved by them. I am left helpless and as a single mum its really difficult to have finances to pay for these things.