Customer Abuse/Unfair Practices/Warranty avoidance

Good Day. I drive is a Ford fiesta 2018 Model which I purchased, February 2018 brand new. I did not miss any service on this vehicle. (Every 20 000 KM or 12 months basis). (Service plan & inspection records are available) My car has been at the dealership for a month now and they are now refusing to honor "Ford" warranty because of an engine fault which they claim was caused by an incorrect "spark plug" which the supposedly found after stripping the engine down. They now sent me an invoice of an amount of R110 671.98 for an engine which should still be covered under "Ford" warranty. In addition they claim that I am now liable to pay for an amount of R4800 for engine stripping. My car was last serviced on the 28th November 2020 at the kilometre reading of 55495 km. It was serviced based on the 12 months period service requirement. My car started giving issues in July 2021. I took my car to the nearest workshop to get it checked because I could not drive to Middleburg at the time because I did not feel safe. I then took my car to the local workshop and I requested the "local" workshop not to do any mechanical work on the car but just check it for me. I watched them do the check. They found a "spark plug" that was totally and completely burnt up. I then requested them to replace it. I subsequently contacted Ford Middleburg for further assistance. Side note: My car was previously towed to Groblersdal due to a supposedly "ignition fault" which caused the car not to start while still covered by the service plan. I don’t drive the car too much... the car only has 3 years with only 64767 km on the clock. I do not understand why they take my car when it was running on it's own and now threaten to return it with the engine on the boot? I feel violated and would like for Ford South Africa to take responsibility and honor their warranty. This is unacceptable.