Call back.

They can't fix it themselves but they can queue it up to be re-ticketed. If they are really good and you are this close to flight time, they will put you on hold and have it done while you wait.

Don't worry about getting a seat, you still have a reservation.

Here is what is going on: For each segment you fly you need both a reservation on the flight as well as an e-coupon. The collection of e-coupons make up your e-ticket, and designate a specific pair (the origin and destination of the segment). When there is a schedule change that requires placing you on a different flight (e.g. the connection city changes), then when you are reaccommodated the agent is supposed to change your reservation and queue the pnr up to be reticketed. It sounds like only the first part was done. But since the reservation is in place with a seat assignment (I assume that you have a seat assignment) you do not have much to worry about. They can do the reticketing pretty quickly at the airport.

You can also verify what e-coupons you currently have by going to the "My Itineraries" page and click on the refund link. It will display all e-coupons you currently have. Most likely you will find that the ones listed correspond to your original itinerary.