Usually, what happens is that the presentation of a large claim, 6 months into the coverage, causes the insurance company to 1st look at the application.
Behind most of the sob-stories you hear, what we find (for example) is a morbidly obese woman, a smoker with history of a heart condition, that listed her health as : weight as 110#, a non-smoker, with perfect health.
I've never heard of a company that cancelled coverage for making a claim. It often happens when fraud has been perpetrated, though.