Usually, when your insurance company/employer makes changes to your insurance coverage, the changes go into effect January 1st. (We have had changes occur in July, as well, so I suppose they can happen at any time.)
Funny, though, you may not be notified of those changes for 30 days or more after they go into effect... Then surprise! You're not covered like you thought you were and get a big fat medical bill.
Case in point: Our insurance required me to report any pregnancy within 3 months of conception or they could deny coverage. I followed the rules. January 12 (today's her 11th birthday) my daughter was born.
Shortly thereafter, I received a HUGE bill on her birth. Huh? I followed the rules... Turns out, our coverage had changed January 1st, but we had not been notified. It was not pretty.
I sent the insurance company a letter pointing out that as I had been required to report the pregnancy at least 6 months in advance, they were well aware of the fact that I would be using the maternity coverage in January. I felt they were morally, if not legally, obligated to have informed me prior to the birth of any changes in coverage.
They paid it as originally covered.
Think you're getting ripped off? Fight it!
It's hard work composing letters, sending them certifed and keeping track of who you've talked to and when. But it's worth it. Document everything. Don't give up.
Have you fought hard, but are being ignored when you know you're right? Contact the Department of Insurance in your state. This governmental agency is there to help straighten out messes and they do a good job.