refuse to refund or replace

I bought a used Pfaff Creative Vision 5.0 from Intersew cc in Magaliesburg in June 2014 and was given a 6 month full guarantee. From the first day I received the machine it broke and shredded the embroidery cotton. The machine was returned twice. I asked for a refund or replace which was ignored the machine was again returned to me and I was told the problem was fixed. Well it was a temporary fix 3-4 months on its back to the same problems. They ignore my requests for refund or replace. People on the pfaff yahoo group are all complaining of the same problem say its a design flaw with the creative vision 5.0. I have paid R50 000 for a machine with a design flaw.