Nightmare plumbers

We asked for quotes in person, verbally, twice, and were promised that they would let us know before proceeding. However the plumbers completed their work without asking us. The plumbers could therefore make up any price and force us to pay. They did end up asking us an exhorbitant price of R 1 900 for 20 minutes worth of work. When I told the boss I was very unhappy (over the phone) and queried the price he immediately assumed we wouldnt pay and started shouting at me. He said that his workers wouldn’t leave our property until we’d made full payment and that they would pour cement down our drain. He called me names and was very mean and aggressive. His workers only left after I had called security and I had started to phone the police. He sent me aggressive messages that night. I was upset because I had my baby with me the whole time and am a bit traumatized.