"I found out I was only eligible to contribute the individual amount because unbeknownst to me my husband was automatically enrolled in Medicare in all of those years."
That is false. What counts is how you were covered. If you were covered by a family HDHP, and you had no "other coverage", then you are eligible to contribute up to the family limit, no matter how your spouse is covered.
(For example, you might have a family HDHP from your employer that covers your spouse because you didn't know your spouse had Medicare, or you might have family coverage from your employer that provides backup coverage to your spouse and helps pay for costs that Medicare doesn't cover. Either way, what counts is how you are covered.)
