Bad service and broken trust

I bought a lounge suite at Lewis Stores in Polokwane on 13 December 2014. I have been experiencing problems with this furniture since June. On 26 June 2015 I called the store to come and collect the 2-seater and 1-seater because they were making a squeaky sound when people sit on them. They took them and they brought them back on 14 July. I found out that they weren't fixed properly. I called the store again and they sent someone on 2 August to come and verify my complaint. They organised for someone to collect the sofas on 12 August. On 14 August, I called the head office to complain about the treatment that I'm getting. I explained that I don't want the sofas anymore because every time they promise that they are fixed and only to find out that they are not. I feel that since our trust and relationship is compromised, even if they are fixed now they will still give me problems in the future. I want the store to give my money back because I can't trust them anymore. A lady from head office (I have her name) told me that she cannot promise to give me my money back because RC told her that the sofas are fixed now. How can I believe this?