"Missing in action" - no response from LAPTOP KING (Seller)

I found a laptop on FB Marketplace as advertised by Jacques Petrie - Laptop King in Boston, Bellville. Dr Johan Bosch bought this laptop on 13 March and eventhough it was advertised with a 8 RAM it only had 4 RAM. I requested several times (via WhatsApp) that Jacques Petrie forward the serial number of the laptop to me for insurance purposes as it was not visible on the laptop. This was never done. Dr Bosch realized that the laptop did not have the 8 RAM and the screen was scratched. He returned the laptop to Jacques Petrie to add the additional RAM and fix the screen (as agreed by them). At this stage Jacques still has the laptop and the money that he already received on 13 March. He does not reply to any messages from Dr Bosch.