If your husband had in fact been provided with dental coverage--even if he did not in fact use it--then he has to pay for it, as per the agreement in place when he signed up for it. If due to an error, he did not pay it at the time, the company may seek its payment now; from what you write, it would therefore seem that your husband is responsible for the back amount. Insurance is inherently a gamble--there's always the chance you'll pay for benefits you don't need, just as there's always a chance you'll receive far more in benefits than you paid. Whether or not you made use of your coverage has no bearing on the obligation to pay.