Threatening and poor quality of work - not worth it

Mass glass aluminum Owner name: Msizi P Zwane The prices in comparison to other aluminum suppliers is good. However the turn around time is longer than they indicate and most importantly the service and installation is poor. They installed a Sliding stacking door and window for me, they followed incorrect installing procedures and took shortcuts, they damaged the window on installation and bent the frame as well as installing skew. I did not pay them until they completed the works and came back to fix, they came back after 2 days of contacting them. They also ignore your calls. They “fixed” the problem in their view but the installation and product is still poor in the end. I wanted to hold money until it was fully fixed but they were threatening to come to the property and tear up their works and remove it from site. Threats included messages as: “ I want my money paid before 1300hrs. I am a black dude and I don't **** with the law. I will go get my door if I don't get my money by 1300hrs. This is not a joke” “ I want the proof sent to me at 1300hrs am boiling I will act like a ******** should you fail to sort out your house” “ Have scratched the door so that you can tell me nonsense. I will give you your life time experience.s piece of a war”