Plumbing Issue at Lufhereng Joscho flats

I have been struggling with sewage for over a month in my unit at Joscho flats in Lufhereng and my health is put at risk. Different plumbers have been sent out, but the matter is still not resolved. Further investigation was done from my end, only to discover that the plumbing was done incorrectly as small pipes were used, meaning the whole plumbing needs to be changed as other units are also flooded with the mess. Question is which inspectors checked the plumbing and how do they approve such small pipes to be used for 407 units. Please help something is wrong.