I agree with Mountain's post.

I would add that I think you can pay DL $50 to take over the ticket. That way they can deal with the issue without having to go through the travel agent. Depending on the TA, and your relationship with them, it might be worth the $50 (which is basically covering the discount the give the TA for selling the ticket).

DL should be able to fix it as long as seats are available on the original route.