You can — and likely should — challenge the insurer’s denial of your disability claim, so long as the claim is otherwise legitimate.
In Illinois (and in other jurisdictions), whenever there is genuine ambiguity in the language of an insurance exclusion clause, the courts are required to strictly construe that ambiguity in favor of the policyholder. Given the fact that courts strictly construe ambiguity in favor of the policyholder and against the interests of the insurer, your insurer is likely to argue that there is no ambiguity.
That being the case, it’s important to work with one of our Chicago disability claim lawyers who has experience handling such disputes — he or she will have to gather and introduce outside evidence that can be used to support your “ambiguity” argument.