Hello and and thank you for your question. For over 34 years, I have answered questions just like yours. And I look forward to assisting you.
Thanks for your question. Please note that before I answer, the answer that I provide is not always what someone wants to hear. But likewise I trust that you will respect that you came here for legal advice even when it is not what you may agree with. So here goes:
As you said, when you enrolled, you did not realize that you had coverage through your husband's work. Likewise, the SSA did not know that either. Therefore, they provided benefits for you. And your benefits were cancelled when you advised them to do so. But you are still liable, and they do not have to reimburse you for the time that you had double coverage. Sorry. Thanks for understanding.