Not allowing me my right to refund

I had purchased a PS4 on the 28 September 2015, and since then I have had to take it back to Makro for repalcement as it is not functioning correctly. The playstation lags and does not function correctly whereby it slows down after some time of play when it comes to a part of a game that requires alot of processing power, for instance when playing Need for Speed 2015, as soon as there is more than 2 cars on the screen or theres tyre smoke coming up, it starts to lag, making it unplayable. As soon as this occurs for the first time, for eg, when I am playing on a Sunday, any day after that, it starts happening more frequently and with shorter play times. After some time, it starts doing this immediately after putting it on for the first time in the day.(same issue with both PS4s). When I had booked in my second unit, I had informed the lady that I either wanted a refund or the newer version of the PS4 which does not have heating issues. I was however given a replacement of the old version. I am not going to accept this, as per CPA section 55 and 56, I have the choice of a refund, but i was informed by Prasilla that I can not have a refund even though its within the 6 months.