Faulty spark plugs, not listed on Dekra report

I bought the car at WebuyCars Silverlakes, it was couriered to me in Cape Town, at the Richmond branch, signed the offer to purchase on the 26th of Feb 2025. On the 12th of August 2025, my car just didnt want to start, I called the sales guy Yaseen, who hasn't called back or returned any of my texts till now. I then called the manufacturer FIAT, as my car is still under warranty, after 3 days they called to advice, the spark plugs need to be replaced and that doesn't fall part of mechanical warranty. My car was due for service in 2weeks, they advised they would do the service and claim from my service plan. Later on they called to advice the service plan wont be covering the cost for the spark plugs, as they were supposed to be replaced at the previous service which was done in September 2024. FIAT try to get hold of the dealership that did the previous service, but that dealership is under new ownership and they dont have previous records. I contacted the sales man again at the silverlakes branch and he still didnt get back to me, I then got hold of his manager Christian, who was very helpful, he told me to log a concern on the website and forward him the quote and the reference number of my complaint and he would escalate. To cut a long story short, it was escalated to a person name Vino Ragolane, who then advised they will not be paying for these spark plugs as its part of service. When i bought the car from we buy cars, it was platinum status, the dekra report stated everything is perfect with the car, service is up to date, there were no wear or tear defect stated, spark plugs weren't listed as faulty. So how am i liable for a service that was done incorrectly a whole year before i even owned the car. Stating "service is up to date" literally means proper service was done. That's not what happened in this case.