You are really going to need an attorney to help you out with this. The facts you supply are helpful, but not sufficient to make any definitive answer. The primary question will turn on the employer's health care coverage procedures and policies. The answer will likely be found buried deeply in the definitions section -- if "separated" is defined under the procedures then that definition will likely control the answer. If "separated" is not defined then it would seem that since you are still legally married, that definition would control.
If you think that your husband has any influence over the employer, you could start by asking him to see if he can find out what the problem is. The real issue is money of course -- the employer doesn't want to pay the insurance premiums for you if they can get out of it. Your husband might actually not bear any fault for this, so if try to work the problem together it might actually help out.
You need to act quickly, since (as you note) there is a timer running on your COBRA payment. Many attorneys offer a free or low-cost initial consultation. Even such an initial consultation might give you a better idea of your options going forward.
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