I would call or write to the HR department and demand that they make you whole, meaning, that you do not absorb the finacial responsiblity for thier error. Tell them you consider this thier error, and they have a responsiblity to fix it, or you will report them to the insurance commision and seek mediation, and if necessary, seek an court order to gain your benefits, and hold them responsible for your attornys fees.
Some thing like this happend to us when my husband went on deployment, and the company HR department suspended a payment while he was gone, and then faild to restart it once he came back, causing us a huge tax bill. At first, they would not deal with me, and said that there was nothing they could do, and then when I insisted, and wrote to them saying that this was thier mistake, and that the only solution I would accept was for them to put us back in the posisition that we would have been in had they not made the error, they relented, and took care of things, though it cost them some money. It is their mistake, go over thier heads.
M.