Worst service

We bought a lounge suite from Lewis stores Despatch. After 3-4 days use the 1 couch (wooden part) collapsed We informed the store that we need to get an exchange. They have exchanged the 1 couch with another one but second hand couch and not a new one. We went back to them and ask that we want our money back. Lady informed me that this could not happen as its longer then our 7 days money back guarantee. But I have informed them within 4 days that the one couch has collapsed the wooden part. Lady also informed me that the lounge suite we have is out of range and cannot get me a new lounge suite. But they can replace it with another lounge suite but im not interested. This is the worst / terrible service I ever got from any store. I do not want another lounge suite I want my money back.