It's an anti-fraud measure and DKR is perhaps the most fraud prone location in the world.

Call back, get a supervisor. DL may be able to verify that your new card # is associated with the same account as the old # and allow you to present the new card.

Alternatively, a supervisor may be able to override the system and allow a new ticket to be issued in the same fare bucket and at the same price as the old ticket and then cancel and refund the old ticket.