Poor customer service and dismissal of Consumer's rights in terms of the Consumer Protection Act

I purchased one DDR3 8GB RAM stick from FirstShop by placing an order on the website and paying via card on 15 March 2023. Upon delivery of the item, I carefully opened the packaging, ensuring that I do not damage the packaging in such a way, that the packaging could be resealed, in case I need to return the item (I have pictures available of the packaging after I opened it). I then installed the RAM in my pc and found that the PC does not want to start-up with the RAM installed, but starts up normally with the old 2GB RAM stick installed. I subsequently called FirstShop and explained the problem, where I was then told the I cannot return the item to FirstShop myself and that I have to log a return by sending an e-mail to *** and cc ***. I subsequently logged a return for the item within 10 working days, whereafter I was told that a collection would be scheduled. The item was however only collected on 11 May 2023. I then subsequently waited patiently for FirstShop to complete their processes and only received feedback from FirstShop on 05 June 2023 via an email, stating that I ordered the incorrect RAM for my PC and that because I opened the packaging, that the item cannot be exchanged or refunded and will be returned to me. When I requested an explanation in this regard and how this decision relate to the Consumer Protection Act of South Africa, Act No.68 of 2008, I was referred to the refund policy of FirstShop where it states that any product opened cannot be credited. When I enquired whether I could exchange the item for another item I could use and that I am not requesting a refund, the response was that the Item is in an "unsellable condition (opened)" and that the item will be returned to me. This is even after I explained to the representative that I carefully opened the item and that the packaging could be easily be re-sealed by applying some "Pritt" or glue stick to it (with photos of the opened item supp****), and that I believe that I am within my rights, as specified in the Consumer Protection Act, I was simply dismissed and informed that the item will simply be returned to me and that I have no other option.

Could Hellopeter kindly please assist me in this regard and advise whether my understanding of the Consumer Protection Act of South Africa, Act No.68 of 2008 is correct and that I am within my rights to have contacted FirstShop and log the return via e-mail within 10 working days and to request for an exchange/credit.