The policy, if it was a benefit from your employer, is a contract you probably never read. The terms of the contract should provide the circumstances and situations where you qualify for benefits. If you never received a cancellation notice, you probably have coverage. You can clear this up with the insurance company or you can just apply for benefits and wait to see what will happen. You apparently still have your job. If you are disabled, you can submit an application for the STD. Don't worry about cancellation from making a claim. If you don't receive your benefits then you can consult with an insurance lawyer. Just make sure you submit an application according to whatever form you are given and than wait for the insurance company to make the next move.
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