Poor service with an unfriendly attitude by the manager

We bought a computer at Lemon Tree in Alberton City . The computer was not working, and we took it back to the store the following day. A week later when we went to fetch it were informed that it was taken back to the supplier. After week when we went again, it was only then when we were informed that it will take 7 -21 days before we know results. We bought the computer because we wanted to use it however it was as if we took our OLD computer for repairs. It was only when we complained that it was taking too long and demanded a refund that they offered a different computer. They said we should top up with R2100 however when we went to pay the cost was now R2150. The manager did not want to acknowledge instead was justifying as if they were right.