You should contact the attorney representing you in the divorce. Generally spousal support orders provide for one of the parties to pay for health insurance if there is insurance when the divorce is filed. I am not aware of any cases involving Medicare supplements, and it is likely he did this because it is the time of year for electing benefits.
I really think you need to talk to an attorney who can fully understand your situation and advocate for you. There are programs for seniors for reduced fee representation. Contact your county bar association to find help.