Originally Posted by MSPeconomist

You were changing the date, so it could not have been done as SDC. [DL rules are different from other airlines on this.]

D is a pretty high fare class, but J means full fare and last seat availability.

Your H fare probably had a $200 change fee, so the charge should have been something like $1700 + $200 - $600 = $1300, where the $600 is roughly half of the price of your original ticket, which would have been the residual value since you seem to have paid the same fare in both directions. This is in addition to the original ticket you purchased.

If you only paid about a thousand dollars, chances are that the phone agent waived the change fee, perhaps because you were forced to buy such an expensive fare. DL agents sometimes do that, especially since you're PM.

SORRY, this is wrong. You're being charged twice for the outbound in this calculation. If we do it differently, we would take the fare difference of $1700 - $1200 = $500 and add the $200 change fee to get about $700 for the final answer on how much you should have paid in addition to the first ticket.