Delta Airlines No notification about unaccompanied minor fee. Internet

I purchased 2 round trip direct tickets for my children on delta.com.  At the time I booked their flights I input their ages during the booking process and there was no mention of an unaccompanied minor fee.  They are 15 and 13 and are flying on a direct flight from ATL to LAX.  I was not notified about this fee at the time of the booking on 2 non-refundable tickets, and did not know about it until I tried to check them in.  If I had known there was a $200 additional fee, I would have booked on a different airline that does not charge this fee for children of their age (Southwest, Airtran, United, Continental do not charge this fee for children over 12). 

So to "accommodate" me, delta offers to refund the price of my tickets minus any taxes and fees on the night before they are supposed to travel.  There is no way to get an alternate flight on this short notice, so I am stuck paying the fee.  To make matters worse, they will not allow me to pay the fee online or over the phone, and my ex-wife refuses to to pay it, so now I'm just stuck not being able to see my children again until October.  Thank you Delta, I will immediately be switching my frequent traveler programs to no longer include your service.