The IRS is not bound by your divorce decree. They won't pay any attention to it. As far as the tax law is concerned, if your tax debt was from joint returns that you filed while you were married, you and your ex-husband are equally responsible for the full amount of the debt. The IRS will continue to take any refund you get and apply it to the total debt, until the full amount is paid.
You will have to talk to your divorce lawyer about how to settle this between you and your ex. The IRS is not going to help you.
Innocent spouse relief does not apply to your situation. That's for situations where your spouse cheated on a joint return, and you were not aware of the cheating.
There is also something called an injured spouse form, but that doesn't apply to your situation either. The Injured Spouse Allocation form can only be filed with a joint return, when only one spouse is responsible for the past debt. It protects the other spouse on the joint return, who is not responsible for the debt. But in your case you are legally responsible for the debt, and anyway you are not filing a joint return.
