Do we employees legally have to pay back when the employer made the mistake?

Ok so in January us employees are either adding or dropping dependents or spouses from our health insurance. This year in January my paperwork said it would cost me $86.16 to take myself and one dependent, my daughter every pay check for health insurance which I signed and all was good. They have been taking it out... show more Ok so in January us employees are either adding or dropping dependents or spouses from our health insurance. This year in January my paperwork said it would cost me $86.16 to take myself and one dependent, my daughter every pay check for health insurance which I signed and all was good. They have been taking it out of my check and everything was good. Now today they tell me that they made an error and us employees have to pay it back. They are not fully done with correcting everything but I asked for an estimate on how much I would have to pay back and they told me $2000.00-$3000.00 dollars. They said they would have us sign a paper and they would take it out of our check in increments. I could understand paying the money back if the $86.16 that I signed for wasn't coming out of my check but that's no the case here, Please help!!