Insurance Nightmare!

When I resigned in July I called the benefits dept. of the school district to ask when my end date was for health insurance. They directed me to call NEA Alaska Health trust. I did and told them I had just resigned, and asked when the last day I would be covered. They said the school district should tell me that. I told them I had been directed to them by the school district. They looked me up on the computer and said August 31st. I called again just to make sure, because Ben needed minor surgery and I needed some dental work, again August 31st. I call my other insurance on September 1st to inform them that they are now my primary. They ask for a letter of termination. I call NEA Alaska Health Trust who intern said they would contact the school district because they hadn't heard from them. I get a letter 7 days later stating my coverage ended on May 31st. Apparently while I was home a week or two into my maternity leave a date passed by that I was unaware of. It was a date in the new contract that stated that employees need to resign by a certain date in order to get benefits through the summer. There are so many problems with this scenario 1) I called multiple times and clearly stated when I resigned and asked when my benefits would end. 2)Should a date like that apply to someone who is on medical leave? 3) I would never have gotten that letter in a timely manner if I hadn't called to ask for it myself. 4) The teachers union for which I have paid a lot of dues is not helping me. I have called for legal consultation.