Terrible workmanship and a guarantee that was not honoured

I spent over R40000 repairing a rusted corrugated roof. I was given a 7 year guarantee. Less than a year later the roof was leaking in multiple places and the veranda roof collapsed altogether. After months of complaints someone came to fix it. Those repairs lasted only a few months before the roof collapsed again and other leaks appeared. No matter how many times I contact the contractor or head office, my request for repairs to be carried out in terms of their guarantee, my requests are ignored or my calls are rejected. Unacceptable workmanship, and their guarantee isn't worth the paper it's written in.