Health Insurance coverage after leaving a job.

I think you might have a very serious problem here, and it's an unusual one.  I would very strongly advise talking to a local attorney, as soon as possible, and I would avoid using the insurance from now on, unless your lawyer tells you otherwise.

Your worst case scenario is that you could be charged with theft, because you would not be able to deny knowing that you were getting something for nothing.  It's also possible that when this is discovered -- and it will be, sooner or later -- you will be retroactively dropped from the insurance (because once you were no longer an employee, you weren't eligible for coverage) and repayment of whatever was paid on your behalf will be demanded.  Please don't wait until they come after you, because that will not help you.