I'm very sympathetic to the frustration you are experiencing. However, for those of us who fly huge amounts, we are very familiar with the fact that changes to connecting cities are as deadly as changes to originating or destination cities when it comes to incurring fees. All that said, it seems you were not handled well and the CR person who made the same misinterpretation was being difficult.

Have you tried simply canceling the entire itinerary (assuming you are permitted to withini 14 days), then calling back and re-booking? I have done this many times on paid tickets where there was a $100 change fee but no penalty for full refund. Same thing works with awards ticket.

Hope it helps. And, by the way, write a letter to customer service explaining how you were treated - there are plenty of UA folks who will put customer service over the feelings of their pal in the next cube...