I would presume what happened is that the OP purchased a cheap ticket, but it had to backtrack to Moscow, so was obviously a longer flight than many more direct routes. Then DL.COM flashes the "your flight has changed, you might have a free change" message.

The OP believed DL.COM and tried to change the flight to a better one. Then was told by DL, "sorry, just kidding about the free change".

My suggestion would be for the OP to find some old monitor/screen that needs to thrown out. Pull up dl.com. Put a few rounds through it.

Now, THAT would be stress relief.

P.S., back to the OP. You can always just keep trying to call back. It is an agent based decision, and one might give you a break.