Claim rejected after following procedures in policy

I submitted a claim for my vehicle due to an engine failure. The car started smoking and engine light came on. I followed all the procedures (stopped driving the car and towed it to an RMI Workshop. The assessor advised that they cannot pay out due to it being wear and tear (carbon build up etc). How am I as the driver supposed to know it's wear and tear when I did exactly what your policy advises to do? How can you justify engine failure as wear and tear? What's the use then having a warranty? For a Mechanical Breakdown Warranty, it sure does NOT live up to its name. I would warn against anybody with an AA Mechanical Breakdown warranty to be weary against this. I feel like I have wasted years of monthly premiums only to be told this when I needed it the most. What a disappointment! If I do not get some sort of help on this I would like to cancel my policy with immediate effect.