Happy to take you money, but not happy to honour claims

I made a claim for in internal engine part failure. The expected life span for the part that failed is 250 000 km. My car is on 90 000, with a full service history and no claims or engine issues. The reason for them declining the claim is "carbon" in the engine. Carbon build-up is a normal process in an internal combustion engine due to the available grades of fuel in RSA. The dealership technical report supports a part failure, not related to wear and tear and not related to carbon deposition. AA warranties sent out an assessor that ignored the dealership technical report and blamed the carbon as a way for them to get out of honouring the claim. This company is happy to take you money, but will look for loopholes to get out of paying legitimate claims.