Base made from Planks and Cardboard

I bought a bed from Beds for Africa, in November 2012. The base literally collapsed in November 2015. I was advised that there is only a 2 year guarantee period, which I accepted. W opened the base to see whether we could fix it ourselves, but to our surprise we noticed that the base was made out of planks and a single layer of cardboard. Surprisingly, the base lasted for 3 years. Beds for Africa sent someone to assess the bed and we were advised that it'll cost us another R1200 for a new base. I have sent several reminders but my emails are not responded to. They also advised that all their bases are made the same - from planks and cardboard. All I want, is a replacement or they need to repair the base. I simply do not believe that we should pay R1400 for a base that is made out of inferior material. We were also asked what our weight was so they could assess whether there was any abuse.