Restonic Bed - Most terrible service EVER !!!

I bought a Restonic bed in December 2013. In May 2014, I reported the bed as defective seeing that the spring inside the matrass seems to be out. The bed made a huge hump on the outside of the matrass at the foot end of the bed. After numerous calls, countless visits to the store, the problem STILL haven't been fixed. I've received calls stating that my new bed has been ordered and I will receive a call as soon as delivery can be arranged, which just NEVER happens. I'm paying every month for a defective bed. I've never been behind on any of my instalments and this is the service that I receive??? I've spoken to a stock clerk, the branch manageres as well as the relieving branch manageres, but nothing gets done!!!